diff --git a/jest.setup.cjs b/jest.setup.cjs
index 97146163b..d9e1df3b6 100644
--- a/jest.setup.cjs
+++ b/jest.setup.cjs
@@ -12,3 +12,4 @@ process.env.UPLOADER_URL = 'https://test-uploader.cdp-int.defra.cloud'
 process.env.UPLOADER_BUCKET_NAME = 'dummy-bucket'
 process.env.GOOGLE_ANALYTICS_TRACKING_ID = 'G-123456789'
 process.env.SUBMISSION_EMAIL_ADDRESS = 'dummy@defra.gov.uk'
+process.env.ORDNANCE_SURVEY_API_KEY = 'dummy'
diff --git a/package-lock.json b/package-lock.json
index 60d1c34d2..76f5b8792 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,7 +10,7 @@
       "hasInstallScript": true,
       "license": "SEE LICENSE IN LICENSE",
       "dependencies": {
-        "@defra/forms-model": "^3.0.559",
+        "@defra/forms-model": "^3.0.560",
         "@defra/hapi-tracing": "^1.26.0",
         "@elastic/ecs-pino-format": "^1.5.0",
         "@hapi/boom": "^10.0.1",
@@ -2272,9 +2272,9 @@
       }
     },
     "node_modules/@defra/forms-model": {
-      "version": "3.0.559",
-      "resolved": "https://registry.npmjs.org/@defra/forms-model/-/forms-model-3.0.559.tgz",
-      "integrity": "sha512-dSMrTnhUXnapflHKdeQLMGDwK2QlFhp/08XwzLNHzLHmgx7pqHAgelzVeRsyHtzYDu7B7tF4r5cyR+SxI4UmXw==",
+      "version": "3.0.560",
+      "resolved": "https://registry.npmjs.org/@defra/forms-model/-/forms-model-3.0.560.tgz",
+      "integrity": "sha512-NQF3EUJmKBwhCypVftLVg+3ZUt0urp0ZdZNG/NaBGx5VwuhVP/MR+TlcXe44xolu8S1PCwN6RtOxGlawzKh9Ew==",
       "license": "OGL-UK-3.0",
       "dependencies": {
         "@joi/date": "^2.1.1",
@@ -2358,40 +2358,6 @@
         "node": ">=10"
       }
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-      "resolved": "https://registry.npmjs.org/@emnapi/core/-/core-1.4.5.tgz",
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-        "tslib": "^2.4.0"
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-    "node_modules/@emnapi/runtime": {
-      "version": "1.4.5",
-      "resolved": "https://registry.npmjs.org/@emnapi/runtime/-/runtime-1.4.5.tgz",
-      "integrity": "sha512-++LApOtY0pEEz1zrd9vy1/zXVaVJJ/EbAF3u0fXIzPJEDtnITsBGbbK0EkM72amhl/R5b+5xx0Y/QhcVOpuulg==",
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "dependencies": {
-        "tslib": "^2.4.0"
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-      "version": "1.0.4",
-      "resolved": "https://registry.npmjs.org/@emnapi/wasi-threads/-/wasi-threads-1.0.4.tgz",
-      "integrity": "sha512-PJR+bOmMOPH8AtcTGAyYNiuJ3/Fcoj2XN/gBEWzDIKh254XO+mM9XoXHk5GNEhodxeMznbg7BlRojVbKN+gC6g==",
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "dependencies": {
-        "tslib": "^2.4.0"
-      }
-    },
     "node_modules/@es-joy/jsdoccomment": {
       "version": "0.49.0",
       "resolved": "https://registry.npmjs.org/@es-joy/jsdoccomment/-/jsdoccomment-0.49.0.tgz",
@@ -3886,19 +3852,6 @@
         "node": ">=18"
       }
     },
-    "node_modules/@napi-rs/wasm-runtime": {
-      "version": "0.2.12",
-      "resolved": "https://registry.npmjs.org/@napi-rs/wasm-runtime/-/wasm-runtime-0.2.12.tgz",
-      "integrity": "sha512-ZVWUcfwY4E/yPitQJl481FjFo3K22D6qF0DuFH6Y/nbnE11GY5uguDxZMGXPQ8WQ0128MXQD7TnfHyK4oWoIJQ==",
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "dependencies": {
-        "@emnapi/core": "^1.4.3",
-        "@emnapi/runtime": "^1.4.3",
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-      }
-    },
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       "version": "2.1.5",
       "resolved": "https://registry.npmjs.org/@nodelib/fs.scandir/-/fs.scandir-2.1.5.tgz",
@@ -4161,17 +4114,6 @@
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-      "resolved": "https://registry.npmjs.org/@tybys/wasm-util/-/wasm-util-0.10.0.tgz",
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-      "dev": true,
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       "resolved": "https://registry.npmjs.org/@types/aria-query/-/aria-query-5.0.4.tgz",
@@ -4922,188 +4864,6 @@
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@@ -5132,65 +4892,6 @@
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@@ -14955,193 +14641,6 @@
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-      "cpu": [
-        "arm64"
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-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "darwin"
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-      "engines": {
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-    },
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-      "resolved": "https://registry.npmjs.org/sass-embedded-darwin-x64/-/sass-embedded-darwin-x64-1.89.2.tgz",
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-      "license": "MIT",
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-    "node_modules/sass-embedded-linux-arm": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-linux-arm/-/sass-embedded-linux-arm-1.89.2.tgz",
-      "integrity": "sha512-leP0t5U4r95dc90o8TCWfxNXwMAsQhpWxTkdtySDpngoqtTy3miMd7EYNYd1znI0FN1CBaUvbdCMbnbPwygDlA==",
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-      "dev": true,
-      "license": "MIT",
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-    "node_modules/sass-embedded-linux-arm64": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-linux-arm64/-/sass-embedded-linux-arm64-1.89.2.tgz",
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-      "dev": true,
-      "license": "MIT",
-      "optional": true,
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-      "engines": {
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-    },
-    "node_modules/sass-embedded-linux-musl-arm": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-linux-musl-arm/-/sass-embedded-linux-musl-arm-1.89.2.tgz",
-      "integrity": "sha512-Z6gG2FiVEEdxYHRi2sS5VIYBmp17351bWtOCUZ/thBM66+e70yiN6Eyqjz80DjL8haRUegNQgy9ZJqsLAAmr9g==",
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-      "dev": true,
-      "license": "MIT",
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-      }
-    },
-    "node_modules/sass-embedded-linux-musl-arm64": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-linux-musl-arm64/-/sass-embedded-linux-musl-arm64-1.89.2.tgz",
-      "integrity": "sha512-nTyuaBX6U1A/cG7WJh0pKD1gY8hbg1m2SnzsyoFG+exQ0lBX/lwTLHq3nyhF+0atv7YYhYKbmfz+sjPP8CZ9lw==",
-      "cpu": [
-        "arm64"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "linux"
-      ],
-      "engines": {
-        "node": ">=14.0.0"
-      }
-    },
-    "node_modules/sass-embedded-linux-musl-riscv64": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-linux-musl-riscv64/-/sass-embedded-linux-musl-riscv64-1.89.2.tgz",
-      "integrity": "sha512-N6oul+qALO0SwGY8JW7H/Vs0oZIMrRMBM4GqX3AjM/6y8JsJRxkAwnfd0fDyK+aICMFarDqQonQNIx99gdTZqw==",
-      "cpu": [
-        "riscv64"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "linux"
-      ],
-      "engines": {
-        "node": ">=14.0.0"
-      }
-    },
     "node_modules/sass-embedded-linux-musl-x64": {
       "version": "1.89.2",
       "resolved": "https://registry.npmjs.org/sass-embedded-linux-musl-x64/-/sass-embedded-linux-musl-x64-1.89.2.tgz",
@@ -15159,23 +14658,6 @@
         "node": ">=14.0.0"
       }
     },
-    "node_modules/sass-embedded-linux-riscv64": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-linux-riscv64/-/sass-embedded-linux-riscv64-1.89.2.tgz",
-      "integrity": "sha512-g9nTbnD/3yhOaskeqeBQETbtfDQWRgsjHok6bn7DdAuwBsyrR3JlSFyqKc46pn9Xxd9SQQZU8AzM4IR+sY0A0w==",
-      "cpu": [
-        "riscv64"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "linux"
-      ],
-      "engines": {
-        "node": ">=14.0.0"
-      }
-    },
     "node_modules/sass-embedded-linux-x64": {
       "version": "1.89.2",
       "resolved": "https://registry.npmjs.org/sass-embedded-linux-x64/-/sass-embedded-linux-x64-1.89.2.tgz",
@@ -15193,40 +14675,6 @@
         "node": ">=14.0.0"
       }
     },
-    "node_modules/sass-embedded-win32-arm64": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-win32-arm64/-/sass-embedded-win32-arm64-1.89.2.tgz",
-      "integrity": "sha512-j96iJni50ZUsfD6tRxDQE2QSYQ2WrfHxeiyAXf41Kw0V4w5KYR/Sf6rCZQLMTUOHnD16qTMVpQi20LQSqf4WGg==",
-      "cpu": [
-        "arm64"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "win32"
-      ],
-      "engines": {
-        "node": ">=14.0.0"
-      }
-    },
-    "node_modules/sass-embedded-win32-x64": {
-      "version": "1.89.2",
-      "resolved": "https://registry.npmjs.org/sass-embedded-win32-x64/-/sass-embedded-win32-x64-1.89.2.tgz",
-      "integrity": "sha512-cS2j5ljdkQsb4PaORiClaVYynE9OAPZG/XjbOMxpQmjRIf7UroY4PEIH+Waf+y47PfXFX9SyxhYuw2NIKGbEng==",
-      "cpu": [
-        "x64"
-      ],
-      "dev": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "win32"
-      ],
-      "engines": {
-        "node": ">=14.0.0"
-      }
-    },
     "node_modules/sass-embedded/node_modules/immutable": {
       "version": "5.0.2",
       "resolved": "https://registry.npmjs.org/immutable/-/immutable-5.0.2.tgz",
diff --git a/package.json b/package.json
index 6461b9cd6..bb3a7f793 100644
--- a/package.json
+++ b/package.json
@@ -70,7 +70,7 @@
   },
   "license": "SEE LICENSE IN LICENSE",
   "dependencies": {
-    "@defra/forms-model": "^3.0.559",
+    "@defra/forms-model": "^3.0.560",
     "@defra/hapi-tracing": "^1.26.0",
     "@elastic/ecs-pino-format": "^1.5.0",
     "@hapi/boom": "^10.0.1",
diff --git a/sonar-project.properties b/sonar-project.properties
index 66b27ddef..fa4e914a7 100644
--- a/sonar-project.properties
+++ b/sonar-project.properties
@@ -11,7 +11,7 @@ sonar.javascript.lcov.reportPaths=coverage/lcov.info
 sonar.sourceEncoding=UTF-8
 
 sonar.sources=src,scripts/generate-schema-docs.js
-sonar.exclusions=**/*.test.*,src/server/forms/*
+sonar.exclusions=**/*.test.*,src/server/forms/*,**/__stubs__/*
 sonar.tests=src,test
 sonar.test.inclusions=**/*.test.*
 sonar.cpd.exclusions=**/*.test.*
diff --git a/src/client/stylesheets/application.scss b/src/client/stylesheets/application.scss
index 349c344c2..822869f24 100644
--- a/src/client/stylesheets/application.scss
+++ b/src/client/stylesheets/application.scss
@@ -12,3 +12,17 @@
 .govuk-header__container {
   border-bottom: 10px solid #003d16;
 }
+
+.app-hidden {
+  display: none;
+  visibility: hidden;
+}
+
+.govuk-button--link {
+  @extend %govuk-link;
+  color: $govuk-link-colour;
+  border: none;
+  cursor: pointer;
+  background-color: transparent;
+  @include govuk-font($size: 19);
+}
diff --git a/src/config/index.ts b/src/config/index.ts
index e6300f769..96fe12dac 100644
--- a/src/config/index.ts
+++ b/src/config/index.ts
@@ -252,7 +252,15 @@ export const config = convict({
     format: String,
     default: '',
     env: 'SUBMISSION_EMAIL_ADDRESS'
-  } as SchemaObj<string>
+  } as SchemaObj<string>,
+
+  ordnanceSurveyApiKey: {
+    doc: 'The ordnance survey api key use by the postcode lookup plugin',
+    format: String,
+    nullable: true,
+    default: undefined,
+    env: 'ORDNANCE_SURVEY_API_KEY'
+  } as SchemaObj<string | undefined>
 })
 
 config.validate({ allowed: 'strict' })
diff --git a/src/index.ts b/src/index.ts
index e6809c961..fa8799fd0 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -13,19 +13,20 @@ process.on('unhandledRejection', (error) => {
   throw error
 })
 
+const port = config.get('port')
+const ordnanceSurveyApiKey = config.get('ordnanceSurveyApiKey')
+
 /**
  * Main entrypoint to the application.
  */
 async function startServer() {
-  const server = await createServer()
+  const server = await createServer({ ordnanceSurveyApiKey })
   await server.start()
 
   process.send?.('online')
 
   server.logger.info('Server started successfully')
-  server.logger.info(
-    `Access your frontend on http://localhost:${config.get('port')}`
-  )
+  server.logger.info(`Access your frontend on http://localhost:${port}`)
 }
 
 startServer().catch((error: unknown) => {
diff --git a/src/server/constants.js b/src/server/constants.js
index 42785542d..fd659a09e 100644
--- a/src/server/constants.js
+++ b/src/server/constants.js
@@ -1,2 +1,4 @@
 export const PREVIEW_PATH_PREFIX = '/preview'
 export const FORM_PREFIX = ''
+export const EXTERNAL_STATE_PAYLOAD = 'EXTERNAL_STATE_PAYLOAD'
+export const EXTERNAL_STATE_APPENDAGE = 'EXTERNAL_STATE_APPENDAGE'
diff --git a/src/server/forms/components.json b/src/server/forms/components.json
index b96bea36c..ee9bbe185 100644
--- a/src/server/forms/components.json
+++ b/src/server/forms/components.json
@@ -120,6 +120,13 @@
           "content": "### This is a H3 in markdown\n\n[An internal link](http://localhost:3009/fictional-page)\n\n[An external link](https://defra.gov.uk/fictional-page)",
           "options": {},
           "schema": {}
+        },
+        {
+          "title": "Summary",
+          "path": "/summary",
+          "controller": "SummaryPageController",
+          "components": [],
+          "next": []
         }
       ]
     }
diff --git a/src/server/forms/register-as-a-unicorn-breeder.yaml b/src/server/forms/register-as-a-unicorn-breeder.yaml
index 3c20764c8..3a7a74760 100644
--- a/src/server/forms/register-as-a-unicorn-breeder.yaml
+++ b/src/server/forms/register-as-a-unicorn-breeder.yaml
@@ -56,10 +56,26 @@ pages:
       - name: wZLWPy
         options:
           required: true
+          usePostcodeLookup: true
         type: UkAddressField
-        title: Address
+        title: What is your billing address
+        shortDescription: Billing address
         schema: {}
-        hint: This is a UK address. Users must enter address line 1, town and a postcode
+        hint: This is a UK billing address. Users must enter address line 1, town and a postcode
+      - name: dfTGhD
+        options: {}
+        schema: {}
+        type: MultilineTextField
+        title: Delivery notes
+        hint:
+          Enter some instructions for the delivery person
+      - name: drGHuj
+        options:
+          required: true
+        type: UkAddressField
+        title: What is your delivery address
+        schema: {}
+        hint: This is a UK delivery address. Users must enter address line 1, town and a postcode
     next:
       - path: '/do-you-want-your-unicorn-breeder-certificate-sent-to-this-address'
     section: section
diff --git a/src/server/plugins/engine/components/UkAddressField.test.ts b/src/server/plugins/engine/components/UkAddressField.test.ts
index 784e19c68..aa5853958 100644
--- a/src/server/plugins/engine/components/UkAddressField.test.ts
+++ b/src/server/plugins/engine/components/UkAddressField.test.ts
@@ -91,6 +91,7 @@ describe('UkAddressField', () => {
 
         expect(field.keys).toEqual([
           'myComponent',
+          'myComponent__uprn',
           'myComponent__addressLine1',
           'myComponent__addressLine2',
           'myComponent__town',
@@ -194,7 +195,8 @@ describe('UkAddressField', () => {
             addressLine2: '',
             town: '',
             county: '',
-            postcode: ''
+            postcode: '',
+            uprn: ''
           })
         )
 
@@ -208,7 +210,8 @@ describe('UkAddressField', () => {
             addressLine2: 'Knutsford Road',
             town: 'Warrington',
             county: 'Cheshire',
-            postcode: 'WA4 1HT'
+            postcode: 'WA4 1HT',
+            uprn: ''
           })
         )
 
@@ -218,7 +221,8 @@ describe('UkAddressField', () => {
             addressLine2: '', // Optional field
             town: 'Warrington',
             county: '', // Optional field
-            postcode: 'WA4 1HT'
+            postcode: 'WA4 1HT',
+            uprn: ''
           })
         )
 
@@ -233,7 +237,8 @@ describe('UkAddressField', () => {
             addressLine2: '',
             town: '',
             county: '',
-            postcode: ''
+            postcode: '',
+            uprn: ''
           })
         )
 
@@ -302,7 +307,7 @@ describe('UkAddressField', () => {
           'postal-code'
         ]
 
-        ukAddressField.collection.components.forEach((component) => {
+        ukAddressField.collection.components.slice(1).forEach((component) => {
           const addressFieldOptions =
             component.options as TextFieldComponent['options']
 
@@ -319,7 +324,8 @@ describe('UkAddressField', () => {
         addressLine2: 'Knutsford Road',
         town: 'Warrington',
         county: 'Cheshire',
-        postcode: 'WA4 1HT'
+        postcode: 'WA4 1HT',
+        uprn: '123456789'
       }
 
       it('returns text from state', () => {
@@ -481,7 +487,8 @@ describe('UkAddressField', () => {
       addressLine2: 'Knutsford Road',
       town: 'Warrington',
       county: 'Cheshire',
-      postcode: 'WA4 1HT'
+      postcode: 'WA4 1HT',
+      uprn: ''
     }
 
     const addressLine1Invalid =
@@ -514,7 +521,8 @@ describe('UkAddressField', () => {
               addressLine2: ' Knutsford Road',
               town: ' Warrington',
               county: 'Cheshire',
-              postcode: ' WA4 1HT'
+              postcode: ' WA4 1HT',
+              uprn: ''
             }),
             output: {
               value: getFormData(address),
@@ -527,7 +535,8 @@ describe('UkAddressField', () => {
               addressLine2: 'Knutsford Road ',
               town: 'Warrington ',
               county: 'Cheshire ',
-              postcode: 'WA4 1HT '
+              postcode: 'WA4 1HT ',
+              uprn: ''
             }),
             output: {
               value: getFormData(address),
@@ -540,7 +549,8 @@ describe('UkAddressField', () => {
               addressLine2: ' Knutsford Road \n\n',
               town: ' Warrington \n\n',
               county: ' Cheshire \n\n',
-              postcode: ' WA4 1HT \n\n'
+              postcode: ' WA4 1HT \n\n',
+              uprn: ''
             }),
             output: {
               value: getFormData(address),
@@ -564,7 +574,8 @@ describe('UkAddressField', () => {
               addressLine2: 'Knutsford Road',
               town: 'Warrington',
               county: 'Cheshire',
-              postcode: 'WA4 1HT'
+              postcode: 'WA4 1HT',
+              uprn: ''
             }),
             output: {
               value: getFormData({
@@ -572,7 +583,8 @@ describe('UkAddressField', () => {
                 addressLine2: 'Knutsford Road',
                 town: 'Warrington',
                 county: 'Cheshire',
-                postcode: 'WA4 1HT'
+                postcode: 'WA4 1HT',
+                uprn: ''
               }),
               errors: [
                 expect.objectContaining({
@@ -587,7 +599,8 @@ describe('UkAddressField', () => {
               addressLine2: addressLine2Invalid,
               town: 'Warrington',
               county: 'Cheshire',
-              postcode: 'WA4 1HT'
+              postcode: 'WA4 1HT',
+              uprn: ''
             }),
             output: {
               value: getFormData({
@@ -595,7 +608,8 @@ describe('UkAddressField', () => {
                 addressLine2: addressLine2Invalid,
                 town: 'Warrington',
                 county: 'Cheshire',
-                postcode: 'WA4 1HT'
+                postcode: 'WA4 1HT',
+                uprn: ''
               }),
               errors: [
                 expect.objectContaining({
@@ -610,7 +624,8 @@ describe('UkAddressField', () => {
               addressLine2: 'Knutsford Road',
               town: townInvalid,
               county: 'Cheshire',
-              postcode: 'WA4 1HT'
+              postcode: 'WA4 1HT',
+              uprn: ''
             }),
             output: {
               value: getFormData({
@@ -618,7 +633,8 @@ describe('UkAddressField', () => {
                 addressLine2: 'Knutsford Road',
                 town: townInvalid,
                 county: 'Cheshire',
-                postcode: 'WA4 1HT'
+                postcode: 'WA4 1HT',
+                uprn: ''
               }),
               errors: [
                 expect.objectContaining({
@@ -633,7 +649,8 @@ describe('UkAddressField', () => {
               addressLine2: 'Knutsford Road',
               town: 'Warrington',
               county: countyInvalid,
-              postcode: 'WA4 1HT'
+              postcode: 'WA4 1HT',
+              uprn: ''
             }),
             output: {
               value: getFormData({
@@ -641,7 +658,8 @@ describe('UkAddressField', () => {
                 addressLine2: 'Knutsford Road',
                 town: 'Warrington',
                 county: countyInvalid,
-                postcode: 'WA4 1HT'
+                postcode: 'WA4 1HT',
+                uprn: ''
               }),
               errors: [
                 expect.objectContaining({
@@ -656,7 +674,8 @@ describe('UkAddressField', () => {
               addressLine2: 'Knutsford Road',
               town: 'Warrington',
               county: 'Cheshire',
-              postcode: postcodeInvalid
+              postcode: postcodeInvalid,
+              uprn: ''
             }),
             output: {
               value: getFormData({
@@ -664,7 +683,8 @@ describe('UkAddressField', () => {
                 addressLine2: 'Knutsford Road',
                 town: 'Warrington',
                 county: 'Cheshire',
-                postcode: postcodeInvalid
+                postcode: postcodeInvalid,
+                uprn: ''
               }),
               errors: [
                 expect.objectContaining({
@@ -679,7 +699,8 @@ describe('UkAddressField', () => {
               addressLine2: '',
               town: '',
               county: '',
-              postcode: postcodeInvalid
+              postcode: postcodeInvalid,
+              uprn: ''
             }),
             output: {
               value: getFormData({
@@ -687,7 +708,8 @@ describe('UkAddressField', () => {
                 addressLine2: '',
                 town: '',
                 county: '',
-                postcode: postcodeInvalid
+                postcode: postcodeInvalid,
+                uprn: ''
               }),
               errors: [
                 expect.objectContaining({
@@ -761,7 +783,8 @@ function getFormData(address: FormPayload): FormPayload {
     myComponent__addressLine2: address.addressLine2,
     myComponent__town: address.town,
     myComponent__county: address.county,
-    myComponent__postcode: address.postcode
+    myComponent__postcode: address.postcode,
+    myComponent__uprn: address.uprn
   }
 }
 
@@ -769,15 +792,15 @@ function getFormData(address: FormPayload): FormPayload {
  * UK address session state
  */
 function getFormState(address: FormPayload): FormState {
-  const [addressLine1, addressLine2, town, county, postcode] = Object.values(
-    getFormData(address)
-  )
+  const [addressLine1, addressLine2, town, county, postcode, uprn] =
+    Object.values(getFormData(address))
 
   return {
     myComponent__addressLine1: addressLine1 ?? null,
     myComponent__addressLine2: addressLine2 ?? null,
     myComponent__town: town ?? null,
     myComponent__county: county ?? null,
-    myComponent__postcode: postcode ?? null
+    myComponent__postcode: postcode ?? null,
+    myComponent__uprn: uprn ?? null
   }
 }
diff --git a/src/server/plugins/engine/components/UkAddressField.ts b/src/server/plugins/engine/components/UkAddressField.ts
index aa73936f8..66eb2aebf 100644
--- a/src/server/plugins/engine/components/UkAddressField.ts
+++ b/src/server/plugins/engine/components/UkAddressField.ts
@@ -1,5 +1,10 @@
-import { ComponentType, type UkAddressFieldComponent } from '@defra/forms-model'
+import {
+  ComponentType,
+  type FormComponentsDef,
+  type UkAddressFieldComponent
+} from '@defra/forms-model'
 import { type ObjectSchema } from 'joi'
+import lowerFirst from 'lodash/lowerFirst.js'
 
 import { ComponentCollection } from '~/src/server/plugins/engine/components/ComponentCollection.js'
 import {
@@ -8,14 +13,20 @@ import {
 } from '~/src/server/plugins/engine/components/FormComponent.js'
 import { TextField } from '~/src/server/plugins/engine/components/TextField.js'
 import { type QuestionPageController } from '~/src/server/plugins/engine/pageControllers/QuestionPageController.js'
+import {
+  type FormRequestPayload,
+  type FormResponseToolkit
+} from '~/src/server/plugins/engine/types/index.js'
 import {
   type ErrorMessageTemplateList,
   type FormPayload,
   type FormState,
   type FormStateValue,
   type FormSubmissionError,
-  type FormSubmissionState
+  type FormSubmissionState,
+  type PostcodeLookupExternalArgs
 } from '~/src/server/plugins/engine/types.js'
+import { dispatch } from '~/src/server/plugins/postcode-lookup/routes/index.js'
 
 export class UkAddressField extends FormComponent {
   declare options: UkAddressFieldComponent['options']
@@ -23,13 +34,15 @@ export class UkAddressField extends FormComponent {
   declare stateSchema: ObjectSchema<FormState>
   declare collection: ComponentCollection
 
+  shortDescription: FormComponentsDef['shortDescription']
+
   constructor(
     def: UkAddressFieldComponent,
     props: ConstructorParameters<typeof FormComponent>[1]
   ) {
     super(def, props)
 
-    const { name, options } = def
+    const { name, options, shortDescription } = def
 
     const isRequired = options.required !== false
     const hideOptional = !!options.optionalText
@@ -37,6 +50,16 @@ export class UkAddressField extends FormComponent {
 
     this.collection = new ComponentCollection(
       [
+        {
+          type: ComponentType.TextField,
+          name: `${name}__uprn`,
+          title: 'UPRN',
+          schema: {},
+          options: {
+            required: false,
+            classes: 'hidden'
+          }
+        },
         {
           type: ComponentType.TextField,
           name: `${name}__addressLine1`,
@@ -103,6 +126,7 @@ export class UkAddressField extends FormComponent {
     this.options = options
     this.formSchema = this.collection.formSchema
     this.stateSchema = this.collection.stateSchema
+    this.shortDescription = shortDescription
   }
 
   getFormValueFromState(state: FormSubmissionState) {
@@ -115,7 +139,9 @@ export class UkAddressField extends FormComponent {
       return null
     }
 
-    return Object.values(value).filter(Boolean)
+    return Object.entries(value)
+      .filter(([key, value]) => key !== 'uprn' && Boolean(value))
+      .map(([, value]) => value)
   }
 
   getContextValueFromState(state: FormSubmissionState) {
@@ -140,17 +166,34 @@ export class UkAddressField extends FormComponent {
   getViewErrors(
     errors?: FormSubmissionError[]
   ): FormSubmissionError[] | undefined {
-    return this.getErrors(errors)?.filter(
+    const uniqueErrors = this.getErrors(errors)?.filter(
       (error, index, self) =>
         index === self.findIndex((err) => err.name === error.name)
     )
+
+    // When using postcode lookup, the address fields are hidden
+    // so we replace any individual validation messages with a single one
+    if (this.shouldUsePostcodeLookup() && uniqueErrors?.length) {
+      const { name, shortDescription } = this
+
+      return [
+        {
+          name,
+          path: [name],
+          href: `#${name}`,
+          text: `Enter ${lowerFirst(shortDescription)}`
+        }
+      ]
+    }
+
+    return uniqueErrors
   }
 
   getViewModel(payload: FormPayload, errors?: FormSubmissionError[]) {
     const { collection, name, options } = this
 
     const viewModel = super.getViewModel(payload, errors)
-    let { components, fieldset, hint, label } = viewModel
+    let { fieldset, hint, label } = viewModel
 
     fieldset ??= {
       legend: {
@@ -173,12 +216,30 @@ export class UkAddressField extends FormComponent {
       }
     }
 
-    components = collection.getViewModel(payload, errors)
+    const components = collection.getViewModel(payload, errors)
+
+    // Hide UPRN
+    const uprn = components.at(0)
+
+    if (!uprn) {
+      throw new Error('No UPRN')
+    }
+
+    uprn.model.formGroup = { classes: 'app-hidden' }
+
+    // Postcode lookup
+    const usePostcodeLookup = this.shouldUsePostcodeLookup()
+
+    const value = usePostcodeLookup
+      ? this.getDisplayStringFromState(payload)
+      : undefined
 
     return {
       ...viewModel,
+      value,
       fieldset,
-      components
+      components,
+      usePostcodeLookup
     }
   }
 
@@ -193,6 +254,10 @@ export class UkAddressField extends FormComponent {
     return UkAddressField.getAllPossibleErrors()
   }
 
+  private shouldUsePostcodeLookup() {
+    return !!(this.options.usePostcodeLookup && this.model.ordnanceSurveyApiKey)
+  }
+
   /**
    * Static version of getAllPossibleErrors that doesn't require a component instance.
    */
@@ -218,9 +283,27 @@ export class UkAddressField extends FormComponent {
       TextField.isText(value.postcode)
     )
   }
+
+  static dispatcher(
+    request: FormRequestPayload,
+    h: FormResponseToolkit,
+    args: PostcodeLookupExternalArgs
+  ) {
+    const { controller, component } = args
+
+    return dispatch(request, h, {
+      formName: controller.model.name,
+      componentName: component.name,
+      componentHint: component.hint,
+      componentTitle: component.title || controller.title,
+      step: args.actionArgs.step,
+      sourceUrl: args.sourceUrl
+    })
+  }
 }
 
 export interface UkAddressState extends Record<string, string> {
+  uprn: string
   addressLine1: string
   addressLine2: string
   town: string
diff --git a/src/server/plugins/engine/configureEnginePlugin.ts b/src/server/plugins/engine/configureEnginePlugin.ts
index dba5fa230..aace62854 100644
--- a/src/server/plugins/engine/configureEnginePlugin.ts
+++ b/src/server/plugins/engine/configureEnginePlugin.ts
@@ -21,7 +21,8 @@ export const configureEnginePlugin = async (
     controllers,
     preparePageEventRequestOptions,
     onRequest,
-    saveAndExit
+    saveAndExit,
+    ordnanceSurveyApiKey
   }: RouteConfig = {},
   cache?: CacheService
 ): Promise<{
@@ -38,7 +39,7 @@ export const configureEnginePlugin = async (
 
     model = new FormModel(
       definition,
-      { basePath: initialBasePath },
+      { basePath: initialBasePath, ordnanceSurveyApiKey },
       services,
       controllers
     )
@@ -63,7 +64,8 @@ export const configureEnginePlugin = async (
       preparePageEventRequestOptions,
       onRequest,
       baseUrl: 'http://localhost:3009', // always runs locally
-      saveAndExit
+      saveAndExit,
+      ordnanceSurveyApiKey
     }
   }
 }
diff --git a/src/server/plugins/engine/models/FormModel.ts b/src/server/plugins/engine/models/FormModel.ts
index e6fa7506b..f3802afb4 100644
--- a/src/server/plugins/engine/models/FormModel.ts
+++ b/src/server/plugins/engine/models/FormModel.ts
@@ -77,6 +77,7 @@ export class FormModel {
   values: FormDefinition
   basePath: string
   versionNumber?: number
+  ordnanceSurveyApiKey?: string
   conditions: Partial<Record<string, ExecutableCondition>>
   pages: PageControllerClass[]
   services: Services
@@ -95,7 +96,11 @@ export class FormModel {
 
   constructor(
     def: typeof this.def,
-    options: { basePath: string; versionNumber?: number },
+    options: {
+      basePath: string
+      versionNumber?: number
+      ordnanceSurveyApiKey?: string
+    },
     services: Services = defaultServices,
     controllers?: Record<string, typeof PageController>
   ) {
@@ -150,6 +155,7 @@ export class FormModel {
     this.values = result.value
     this.basePath = options.basePath
     this.versionNumber = options.versionNumber
+    this.ordnanceSurveyApiKey = options.ordnanceSurveyApiKey
     this.conditions = {}
     this.services = services
     this.controllers = controllers
@@ -551,7 +557,9 @@ function validateFormPayload(
   // Skip validation GET requests or other actions
   if (
     !request.payload ||
-    (action && ![FormAction.Validate, FormAction.SaveAndExit].includes(action))
+    (action &&
+      ![FormAction.Validate, FormAction.SaveAndExit].includes(action) &&
+      !action.startsWith(FormAction.External))
   ) {
     return context
   }
diff --git a/src/server/plugins/engine/options.js b/src/server/plugins/engine/options.js
index 3efb29e87..ac1ad1380 100644
--- a/src/server/plugins/engine/options.js
+++ b/src/server/plugins/engine/options.js
@@ -25,7 +25,8 @@ const pluginRegistrationOptionsSchema = Joi.object({
   preparePageEventRequestOptions: Joi.function().optional(),
   onRequest: Joi.function().optional(),
   baseUrl: Joi.string().uri().required(),
-  saveAndExit: Joi.function().optional()
+  saveAndExit: Joi.function().optional(),
+  ordnanceSurveyApiKey: Joi.string().optional()
 })
 
 /**
diff --git a/src/server/plugins/engine/pageControllers/QuestionPageController.test.ts b/src/server/plugins/engine/pageControllers/QuestionPageController.test.ts
index 42c252ae8..7e20e2696 100644
--- a/src/server/plugins/engine/pageControllers/QuestionPageController.test.ts
+++ b/src/server/plugins/engine/pageControllers/QuestionPageController.test.ts
@@ -602,6 +602,7 @@ describe('QuestionPageController', () => {
         addressField__town: 'Town or city',
         addressField__county: 'Cheshire',
         addressField__postcode: 'CW1 1AB',
+        addressField__uprn: '',
         radiosField: 'privateLimitedCompany',
         selectField: 910400000,
         autocompleteField: 910400044,
diff --git a/src/server/plugins/engine/pageControllers/QuestionPageController.ts b/src/server/plugins/engine/pageControllers/QuestionPageController.ts
index b912a6449..20ef943ae 100644
--- a/src/server/plugins/engine/pageControllers/QuestionPageController.ts
+++ b/src/server/plugins/engine/pageControllers/QuestionPageController.ts
@@ -12,6 +12,10 @@ import Boom from '@hapi/boom'
 import { type RouteOptions } from '@hapi/hapi'
 import { type ValidationErrorItem } from 'joi'
 
+import {
+  EXTERNAL_STATE_APPENDAGE,
+  EXTERNAL_STATE_PAYLOAD
+} from '~/src/server/constants.js'
 import { ComponentCollection } from '~/src/server/plugins/engine/components/ComponentCollection.js'
 import { optionalText } from '~/src/server/plugins/engine/components/constants.js'
 import { type BackLink } from '~/src/server/plugins/engine/components/types.js'
@@ -35,6 +39,7 @@ import {
   type FormStateValue,
   type FormSubmissionState
 } from '~/src/server/plugins/engine/types.js'
+import { getComponentsByType } from '~/src/server/plugins/engine/validationHelpers.js'
 import {
   FormAction,
   type FormRequest,
@@ -492,6 +497,11 @@ export class QuestionPageController extends PageController {
     ) => {
       const { collection, viewName, model } = this
       const { isForceAccess, state, evaluationState } = context
+      const action = request.payload.action
+
+      if (action?.startsWith(FormAction.External)) {
+        return this.dispatchExternal(request, h, context)
+      }
 
       /**
        * If there are any errors, render the page with the parsed errors
@@ -515,7 +525,6 @@ export class QuestionPageController extends PageController {
       await this.setState(request, state)
 
       // Check if this is a save-and-exit action
-      const { action } = request.payload
       if (action === FormAction.SaveAndExit) {
         return this.handleSaveAndExit(request, context, h)
       }
@@ -525,6 +534,65 @@ export class QuestionPageController extends PageController {
     }
   }
 
+  private dispatchExternal(
+    request: FormRequestPayload,
+    h: FormResponseToolkit,
+    context: FormContext
+  ) {
+    const { externalComponents } = getComponentsByType()
+    const action = request.payload.action ?? ''
+
+    // Find the external action and arguments
+    // `external-{componentName}--{argname1}:{argvalue1}--{argname2}:{argvalue2}`
+    // E.g. external-abcdef--amount:10--step:manual
+    const externalActionsWithArgs = action
+      .slice(`${FormAction.External}-`.length)
+      .split('--')
+
+    const externalActionArgs = externalActionsWithArgs
+      .slice(1)
+      .map((arg) => arg.split(':'))
+
+    const args = Object.fromEntries(externalActionArgs) as Record<
+      string,
+      string
+    >
+
+    const componentName = externalActionsWithArgs[0]
+    const component = this.model.componentDefMap.get(componentName)
+    const componentType = component?.type
+
+    if (!componentType) {
+      throw Boom.internal(
+        `External component of type ${componentType} not found`
+      )
+    }
+
+    const selectedComponent = externalComponents.get(componentType)
+
+    if (!selectedComponent) {
+      throw Boom.internal(`External component ${componentName} not found`)
+    }
+
+    // Stash payload without crumb and action
+    const stashedPayload = {
+      ...context.payload,
+      crumb: undefined,
+      action: undefined
+    }
+    request.yar.flash(EXTERNAL_STATE_PAYLOAD, stashedPayload, true)
+
+    // Clear any previous state appendage
+    request.yar.clear(EXTERNAL_STATE_APPENDAGE)
+
+    return selectedComponent.dispatcher(request, h, {
+      component,
+      controller: this,
+      sourceUrl: request.url.toString(),
+      actionArgs: args
+    })
+  }
+
   proceed(
     request: FormContextRequest,
     h: FormResponseToolkit,
diff --git a/src/server/plugins/engine/plugin.ts b/src/server/plugins/engine/plugin.ts
index a20451f16..14b915bf5 100644
--- a/src/server/plugins/engine/plugin.ts
+++ b/src/server/plugins/engine/plugin.ts
@@ -15,6 +15,7 @@ import { getRoutes as getRepeaterItemDeleteRoutes } from '~/src/server/plugins/e
 import { getRoutes as getRepeaterSummaryRoutes } from '~/src/server/plugins/engine/routes/repeaters/summary.js'
 import { type PluginOptions } from '~/src/server/plugins/engine/types.js'
 import { registerVision } from '~/src/server/plugins/engine/vision.js'
+import { postcodeLookupPlugin } from '~/src/server/plugins/postcode-lookup/index.js'
 import {
   type FormRequestPayloadRefs,
   type FormRequestRefs
@@ -35,7 +36,8 @@ export const plugin = {
       nunjucks: nunjucksOptions,
       viewContext,
       preparePageEventRequestOptions,
-      onRequest
+      onRequest,
+      ordnanceSurveyApiKey
     } = options
 
     const cacheService =
@@ -45,6 +47,16 @@ export const plugin = {
 
     await registerVision(server, options)
 
+    // Register the postcode lookup plugin only if we have an OS api key
+    if (ordnanceSurveyApiKey) {
+      await server.register({
+        plugin: postcodeLookupPlugin,
+        options: {
+          ordnanceSurveyApiKey
+        }
+      })
+    }
+
     server.expose('baseLayoutPath', nunjucksOptions.baseLayoutPath)
     server.expose('viewContext', viewContext)
     server.expose('cacheService', cacheService)
diff --git a/src/server/plugins/engine/routes/index.test.ts b/src/server/plugins/engine/routes/index.test.ts
index 826ccef48..45cb49128 100644
--- a/src/server/plugins/engine/routes/index.test.ts
+++ b/src/server/plugins/engine/routes/index.test.ts
@@ -25,6 +25,7 @@ describe('redirectOrMakeHandler', () => {
   const mockRequest: AnyFormRequest = {
     server: mockServer,
     app: {},
+    yar: { flash: () => [] },
     params: { path: 'test-path' },
     query: {}
   } as unknown as AnyFormRequest
diff --git a/src/server/plugins/engine/routes/index.ts b/src/server/plugins/engine/routes/index.ts
index 37225060a..e4e765706 100644
--- a/src/server/plugins/engine/routes/index.ts
+++ b/src/server/plugins/engine/routes/index.ts
@@ -6,7 +6,15 @@ import {
 } from '@hapi/hapi'
 import { isEqual } from 'date-fns'
 
-import { PREVIEW_PATH_PREFIX } from '~/src/server/constants.js'
+import {
+  EXTERNAL_STATE_APPENDAGE,
+  EXTERNAL_STATE_PAYLOAD,
+  PREVIEW_PATH_PREFIX
+} from '~/src/server/constants.js'
+import {
+  FormComponent,
+  isFormState
+} from '~/src/server/plugins/engine/components/FormComponent.js'
 import {
   checkEmailAddressForLiveFormSubmission,
   checkFormStatus,
@@ -22,7 +30,10 @@ import { generateUniqueReference } from '~/src/server/plugins/engine/referenceNu
 import * as defaultServices from '~/src/server/plugins/engine/services/index.js'
 import {
   type AnyFormRequest,
+  type ExternalStateAppendage,
   type FormContext,
+  type FormPayload,
+  type FormSubmissionState,
   type OnRequestCallback,
   type PluginOptions
 } from '~/src/server/plugins/engine/types.js'
@@ -66,6 +77,8 @@ export async function redirectOrMakeHandler(
     })
   }
 
+  state = await importExternalComponentState(request, page, state)
+
   const flash = cacheService.getFlash(request)
   const context = model.getFormContext(request, state, flash?.errors)
   const relevantPath = page.getRelevantPath(request, context)
@@ -95,11 +108,66 @@ export async function redirectOrMakeHandler(
   return proceed(request, h, page.getHref(relevantPath))
 }
 
+async function importExternalComponentState(
+  request: AnyFormRequest,
+  page: PageControllerClass,
+  state: FormSubmissionState
+): Promise<FormSubmissionState> {
+  const externalComponentData = request.yar.flash(EXTERNAL_STATE_APPENDAGE)
+
+  if (Array.isArray(externalComponentData)) {
+    return state
+  }
+
+  const typedStateAppendage = externalComponentData as ExternalStateAppendage
+  const componentName = typedStateAppendage.component
+  const stateAppendage = typedStateAppendage.data
+  const component = request.app.model?.componentMap.get(componentName)
+
+  if (!component) {
+    throw new Error(`Component ${componentName} not found in form`)
+  }
+
+  if (!(component instanceof FormComponent)) {
+    throw new TypeError(
+      `Component ${componentName} is not a FormComponent and does not support isState`
+    )
+  }
+
+  const isStateValid = component.isState(stateAppendage)
+
+  if (!isStateValid) {
+    throw new Error(`State for component ${componentName} is invalid`)
+  }
+
+  const componentState = isFormState(stateAppendage)
+    ? Object.fromEntries(
+        Object.entries(stateAppendage).map(([key, value]) => [
+          `${componentName}__${key}`,
+          value
+        ])
+      )
+    : { [componentName]: stateAppendage }
+
+  // Save the external component state immediately
+  const updatedState = await page.mergeState(request, state, componentState)
+
+  // Merge the stashed payload into the local state
+  const payload = request.yar.flash(EXTERNAL_STATE_PAYLOAD)
+  const stashedPayload = Array.isArray(payload) ? {} : (payload as FormPayload)
+
+  return { ...stashedPayload, ...updatedState }
+}
+
 export function makeLoadFormPreHandler(server: Server, options: PluginOptions) {
   // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- hapi types are wrong
   const prefix = server.realm.modifiers.route.prefix ?? ''
 
-  const { services = defaultServices, controllers } = options
+  const {
+    services = defaultServices,
+    controllers,
+    ordnanceSurveyApiKey
+  } = options
 
   const { formsService } = services
 
@@ -166,7 +234,7 @@ export function makeLoadFormPreHandler(server: Server, options: PluginOptions) {
       // Construct the form model
       const model = new FormModel(
         definition,
-        { basePath, versionNumber },
+        { basePath, versionNumber, ordnanceSurveyApiKey },
         services,
         controllers
       )
diff --git a/src/server/plugins/engine/types.ts b/src/server/plugins/engine/types.ts
index 00f0e394f..b2dde4e23 100644
--- a/src/server/plugins/engine/types.ts
+++ b/src/server/plugins/engine/types.ts
@@ -4,7 +4,8 @@ import {
   type FormVersionMetadata,
   type Item,
   type List,
-  type Page
+  type Page,
+  type UkAddressFieldComponent
 } from '@defra/forms-model'
 import {
   type PluginProperties,
@@ -28,6 +29,7 @@ import { type FormModel } from '~/src/server/plugins/engine/models/index.js'
 import { type DetailItemField } from '~/src/server/plugins/engine/models/types.js'
 import { type PageController } from '~/src/server/plugins/engine/pageControllers/PageController.js'
 import { type PageControllerClass } from '~/src/server/plugins/engine/pageControllers/helpers/pages.js'
+import { type QuestionPageController } from '~/src/server/plugins/engine/pageControllers/index.js'
 import {
   type FileStatus,
   type FormAdapterSubmissionSchemaVersion,
@@ -378,6 +380,23 @@ export type SaveAndExitHandler = (
   context: FormContext
 ) => ResponseObject
 
+export interface ExternalArgs {
+  component: ComponentDef
+  controller: QuestionPageController
+  sourceUrl: string
+  actionArgs: Record<string, string>
+}
+
+export interface PostcodeLookupExternalArgs extends ExternalArgs {
+  component: UkAddressFieldComponent
+  actionArgs: { step: string }
+}
+
+export interface ExternalStateAppendage {
+  component: string
+  data: FormStateValue | FormState
+}
+
 export interface PluginOptions {
   model?: FormModel
   services?: Services
@@ -395,6 +414,7 @@ export interface PluginOptions {
   preparePageEventRequestOptions?: PreparePageEventRequestOptions
   onRequest?: OnRequestCallback
   baseUrl: string // base URL of the application, protocol and hostname e.g. "https://myapp.com"
+  ordnanceSurveyApiKey?: string
 }
 
 export interface FormAdapterSubmissionMessageMeta {
diff --git a/src/server/plugins/engine/validationHelpers.ts b/src/server/plugins/engine/validationHelpers.ts
new file mode 100644
index 000000000..268cf5792
--- /dev/null
+++ b/src/server/plugins/engine/validationHelpers.ts
@@ -0,0 +1,48 @@
+import { type ResponseObject } from '@hapi/hapi'
+
+import * as Components from '~/src/server/plugins/engine/components/index.js'
+import {
+  type FormRequestPayload,
+  type FormResponseToolkit
+} from '~/src/server/plugins/engine/types/index.js'
+import { type ExternalArgs } from '~/src/server/plugins/engine/types.js'
+
+// Type guard for ExternalComponent
+export function isExternalComponent(
+  component: unknown
+): component is ExternalComponent {
+  return typeof (component as ExternalComponent).dispatcher === 'function'
+}
+
+// External components are guaranteed to have a dispatcher method
+export interface ExternalComponent {
+  dispatcher(
+    request: FormRequestPayload,
+    h: FormResponseToolkit,
+    args: ExternalArgs
+  ): ResponseObject
+}
+
+/**
+ * Returns internal and external components from a componentMap, regardless of error state.
+ * @returns An object containing internalComponents and externalComponents arrays
+ */
+export function getComponentsByType(): {
+  internalComponents: Map<string, unknown>
+  externalComponents: Map<string, ExternalComponent>
+} {
+  const internalComponents = new Map<string, unknown>()
+  const externalComponents = new Map<string, ExternalComponent>()
+
+  const componentMap = new Map<string, unknown>(Object.entries(Components))
+
+  for (const [name, component] of componentMap.entries()) {
+    if (isExternalComponent(component)) {
+      externalComponents.set(name, component)
+    } else {
+      internalComponents.set(name, component)
+    }
+  }
+
+  return { internalComponents, externalComponents }
+}
diff --git a/src/server/plugins/engine/views/components/ukaddressfield.html b/src/server/plugins/engine/views/components/ukaddressfield.html
index 12bd4965f..e2aabbe7e 100644
--- a/src/server/plugins/engine/views/components/ukaddressfield.html
+++ b/src/server/plugins/engine/views/components/ukaddressfield.html
@@ -1,10 +1,18 @@
 {% from "partials/components.html" import componentList %}
 {% from "govuk/components/fieldset/macro.njk" import govukFieldset %}
 {% from "govuk/components/hint/macro.njk" import govukHint %}
+{% from "govuk/components/button/macro.njk" import govukButton %}
+{% from "govuk/components/inset-text/macro.njk" import govukInsetText %}
 
 {% macro UkAddressField(component) %}
   {% set fieldset = component.model.fieldset %}
-  {% set addressFieldHtml = componentList(component.model.components) %}
+  {% set usePostcodeLookup = component.model.usePostcodeLookup %}
+
+  {% set addressFieldHtml %}
+    <div {{"hidden" if usePostcodeLookup }}>
+      {{ componentList(component.model.components) }}
+    </div>
+  {% endset %}
 
   {% if component.model.hint %}
     {% set addressHintHtml %}
@@ -17,9 +25,45 @@
     {% set addressFieldHtml = addressHintHtml + addressFieldHtml %}
   {% endif %}
 
-  {{ govukFieldset({
-    legend: fieldset.legend,
-    attributes: fieldset.attributes,
-    html: addressFieldHtml
-  }) if fieldset else addressFieldHtml }}
+  <div id="{{component.model.name}}" class="govuk-form-group{{ ' govuk-form-group--error' if usePostcodeLookup and component.model.errors | length }}">
+    {{ govukFieldset({
+      legend: fieldset.legend,
+      attributes: fieldset.attributes,
+      html: addressFieldHtml
+    }) if fieldset else addressFieldHtml }}
+
+    {% if usePostcodeLookup %}
+      {% set value = component.model.value %}
+
+        {% if value %}
+          {% set insetHtml %}
+            <strong>Selected address:</strong>
+            <br><br>
+            {{ value }}
+            <br><br>
+            <p class="govuk-body">
+              <button class="govuk-link govuk-button--link govuk-!-margin-right-1" name="action"
+                value="external-{{component.model.name}}">Use a different address</button>
+            </p>
+          {% endset %}
+
+          {{ govukInsetText({
+            html: insetHtml,
+            classes: "govuk-!-margin-top-2"
+          }) }}
+        {% else %}
+          <div class="govuk-button-group govuk-!-margin-bottom-0">
+            {{ govukButton({
+              text: "Find an address",
+              attributes: {
+                name: "action",
+                value: "external-" + component.model.name
+              },
+              classes: "govuk-button--secondary govuk-!-margin-right-1 govuk-!-margin-bottom-0"
+            }) }}
+            <p class="govuk-body govuk-!-margin-bottom-0">or <button class="govuk-link govuk-button--link govuk-!-margin-right-1 govuk-!-margin-bottom-0" name="action" value="external-{{component.model.name}}--step:manual">enter address manually</button></p>
+          </div>
+        {% endif %}
+    {% endif %}
+  </div>
 {% endmacro %}
diff --git a/src/server/plugins/engine/vision.ts b/src/server/plugins/engine/vision.ts
index 048aa9481..99a976b2e 100644
--- a/src/server/plugins/engine/vision.ts
+++ b/src/server/plugins/engine/vision.ts
@@ -13,6 +13,7 @@ import {
   prepareNunjucksEnvironment
 } from '~/src/server/plugins/engine/index.js'
 import { type PluginOptions } from '~/src/server/plugins/engine/types.js'
+import { VIEW_PATH as POSTCODE_LOOKUP_VIEW_PATH } from '~/src/server/plugins/postcode-lookup/index.js'
 
 export async function registerVision(
   server: Server,
@@ -24,10 +25,15 @@ export async function registerVision(
   )
 
   const viewPathResolved = join(packageRoot, VIEW_PATH)
+  const postcodeLookupPathResolved = join(
+    packageRoot,
+    POSTCODE_LOOKUP_VIEW_PATH
+  )
 
   const paths = [
     ...pluginOptions.nunjucks.paths,
     viewPathResolved,
+    postcodeLookupPathResolved,
     join(govukFrontendPath, 'dist')
   ]
 
diff --git a/src/server/plugins/postcode-lookup/index.js b/src/server/plugins/postcode-lookup/index.js
new file mode 100644
index 000000000..f9c4ad72b
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/index.js
@@ -0,0 +1,21 @@
+import { getRoutes } from '~/src/server/plugins/postcode-lookup/routes/index.js'
+
+export const VIEW_PATH = 'src/server/plugins/postcode-lookup/views'
+
+/**
+ * @satisfies {NamedPlugin<PostcodeLookupConfiguration>}
+ */
+export const postcodeLookupPlugin = {
+  name: '@defra/forms-engine-plugin/postcode-lookup',
+  dependencies: ['@hapi/vision'],
+  multiple: false,
+  register(server, options) {
+    // @ts-expect-error - Request typing
+    server.route(getRoutes(options))
+  }
+}
+
+/**
+ * @import { NamedPlugin } from '@hapi/hapi'
+ * @import { PostcodeLookupConfiguration } from '~/src/server/plugins/postcode-lookup/types.js'
+ */
diff --git a/src/server/plugins/postcode-lookup/models/index.js b/src/server/plugins/postcode-lookup/models/index.js
new file mode 100644
index 000000000..34593c18a
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/models/index.js
@@ -0,0 +1,549 @@
+import Joi from 'joi'
+
+import * as service from '~/src/server/plugins/postcode-lookup/service.js'
+import { crumbSchema } from '~/src/server/schemas/index.js'
+
+// Field names/ids
+const postcodeQueryFieldName = 'postcodeQuery'
+const buildingNameQueryFieldName = 'buildingNameQuery'
+const uprnFieldName = 'uprn'
+
+const line1FieldName = 'addressLine1'
+const line2FieldName = 'addressLine2'
+const townFieldName = 'town'
+const countyFieldName = 'county'
+const postcodeFieldName = 'postcode'
+
+const selectLabelText = 'Select an address'
+
+const GOVUK_MARGIN_RIGHT_1 = 'govuk-!-margin-right-1'
+
+export const steps = {
+  // Step 1: Postcode/building name input
+  details: 'details',
+  // Step 2: Select address
+  select: 'select',
+  // Step 3: Manual address
+  manual: 'manual'
+}
+
+export const JOURNEY_BASE_URL = '/postcode-lookup'
+
+/**
+ * Build form errors
+ * @param {Error} [err]
+ */
+function buildErrors(err) {
+  const hasErrors = Joi.isError(err) && err.details.length > 0
+
+  if (!hasErrors) {
+    return {}
+  }
+
+  /**
+   * Get error by path
+   * @param {string} fieldName
+   */
+  const getError = (fieldName) => {
+    return err.details.find((item) => item.path[0] === fieldName)
+  }
+
+  const postcodeQueryError = getError(postcodeQueryFieldName)
+  const buildingNameQueryError = getError(buildingNameQueryFieldName)
+  const uprnError = getError(uprnFieldName)
+  const line1Error = getError(line1FieldName)
+  const line2Error = getError(line2FieldName)
+  const townError = getError(townFieldName)
+  const countyError = getError(countyFieldName)
+  const postcodeError = getError(postcodeFieldName)
+
+  /**
+   * @type {{ text: string, href: string }[]}
+   */
+  const errors = []
+
+  /**
+   * Push error
+   * @param {string} fieldName - the field name
+   * @param {ValidationErrorItem} [item] - the joi validation error
+   */
+  const pushError = (fieldName, item) => {
+    if (item) {
+      errors.push({
+        text: item.message,
+        href: `#${fieldName}`
+      })
+    }
+  }
+
+  pushError(postcodeQueryFieldName, postcodeQueryError)
+  pushError(buildingNameQueryFieldName, buildingNameQueryError)
+  pushError(uprnFieldName, uprnError)
+  pushError(line1FieldName, line1Error)
+  pushError(line2FieldName, line2Error)
+  pushError(townFieldName, townError)
+  pushError(countyFieldName, countyError)
+  pushError(postcodeFieldName, postcodeError)
+
+  return {
+    errors,
+    postcodeQueryError,
+    buildingNameQueryError,
+    uprnError,
+    line1Error,
+    line2Error,
+    townError,
+    countyError,
+    postcodeError
+  }
+}
+
+/**
+ * Search ordnance survey for addresses
+ * @param {string} postcodeQuery
+ * @param {string} buildingNameQuery
+ * @param {string} apiKey
+ */
+async function getAddresses(postcodeQuery, buildingNameQuery, apiKey) {
+  const addresses = await service.search(
+    postcodeQuery,
+    buildingNameQuery,
+    apiKey
+  )
+  const addressCount = addresses.length
+  const singleAddress = addressCount === 1 ? addresses.at(0) : undefined
+  const hasAddresses = addressCount > 0
+  const hasMultipleAddresses = addressCount > 1
+
+  return {
+    hasAddresses,
+    hasMultipleAddresses,
+    singleAddress,
+    addresses,
+    addressCount
+  }
+}
+
+/**
+ * Get the details view fields
+ * @param {PostcodeLookupDetailsData | undefined} details
+ * @param {OptionalValidationErrorItem} postcodeQueryError
+ * @param {OptionalValidationErrorItem} buildingNameQueryError
+ */
+function getDetailsFields(details, postcodeQueryError, buildingNameQueryError) {
+  return {
+    [postcodeQueryFieldName]: {
+      id: postcodeQueryFieldName,
+      name: postcodeQueryFieldName,
+      label: {
+        text: 'Postcode'
+      },
+      hint: {
+        text: 'For example, AA3 1AB'
+      },
+      value: details?.postcodeQuery,
+      errorMessage: postcodeQueryError && { text: postcodeQueryError.message }
+    },
+    [buildingNameQueryFieldName]: {
+      id: buildingNameQueryFieldName,
+      name: buildingNameQueryFieldName,
+      label: {
+        text: 'Building name or number (optional)'
+      },
+      hint: {
+        text: 'For example, 15 or Prospect Cottage'
+      },
+      value: details?.buildingNameQuery,
+      errorMessage: buildingNameQueryError && {
+        text: buildingNameQueryError.message
+      }
+    }
+  }
+}
+
+/**
+ * Get the select view fields
+ * @param {PostcodeLookupDetailsData} details
+ * @param {boolean} hasMultipleAddresses
+ * @param {Address | undefined} singleAddress
+ * @param {PostcodeLookupSelectPayload | undefined} payload
+ * @param {OptionalValidationErrorItem} uprnError
+ * @param {Address[]} addresses
+ */
+function getSelectFields(
+  details,
+  hasMultipleAddresses,
+  singleAddress,
+  payload,
+  uprnError,
+  addresses
+) {
+  return {
+    [postcodeQueryFieldName]: {
+      id: postcodeQueryFieldName,
+      name: postcodeQueryFieldName,
+      type: 'hidden',
+      value: details.postcodeQuery
+    },
+    [buildingNameQueryFieldName]: {
+      id: buildingNameQueryFieldName,
+      name: buildingNameQueryFieldName,
+      type: 'hidden',
+      value: details.buildingNameQuery
+    },
+    [uprnFieldName]: {
+      id: uprnFieldName,
+      name: uprnFieldName,
+      label: hasMultipleAddresses
+        ? {
+            text: selectLabelText
+          }
+        : undefined,
+      value: singleAddress ? singleAddress.uprn : payload?.uprn,
+      errorMessage: uprnError && { text: uprnError.message },
+      items: hasMultipleAddresses
+        ? [{ text: selectLabelText, value: '' }].concat(
+            addresses.map((item) => ({
+              text: item.formatted,
+              value: item.uprn
+            }))
+          )
+        : undefined,
+      type: singleAddress ? 'hidden' : undefined
+    }
+  }
+}
+
+/**
+ * Get the manual view fields
+ * @param {PostcodeLookupManualPayload | undefined} payload
+ * @param {OptionalValidationErrorItem} line1Error
+ * @param {OptionalValidationErrorItem} line2Error
+ * @param {OptionalValidationErrorItem} townError
+ * @param {OptionalValidationErrorItem} countyError
+ * @param {OptionalValidationErrorItem} postcodeError
+ */
+function getManualFields(
+  payload,
+  line1Error,
+  line2Error,
+  townError,
+  countyError,
+  postcodeError
+) {
+  return {
+    [line1FieldName]: {
+      id: line1FieldName,
+      name: line1FieldName,
+      label: {
+        text: 'Address line 1'
+      },
+      value: payload?.addressLine1,
+      errorMessage: line1Error && { text: line1Error.message }
+    },
+    [line2FieldName]: {
+      id: line2FieldName,
+      name: line2FieldName,
+      label: {
+        text: 'Address line 2 (optional)'
+      },
+      value: payload?.addressLine2,
+      errorMessage: line2Error && { text: line2Error.message }
+    },
+    [townFieldName]: {
+      id: townFieldName,
+      name: townFieldName,
+      label: {
+        text: 'Town or city'
+      },
+      classes: 'govuk-!-width-two-thirds',
+      value: payload?.town,
+      errorMessage: townError && { text: townError.message }
+    },
+    [countyFieldName]: {
+      id: countyFieldName,
+      name: countyFieldName,
+      label: {
+        text: 'County (optional)'
+      },
+      value: payload?.county,
+      errorMessage: countyError && { text: countyError.message }
+    },
+    [postcodeFieldName]: {
+      id: postcodeFieldName,
+      name: postcodeFieldName,
+      label: {
+        text: 'Postcode'
+      },
+      classes: 'govuk-input--width-10',
+      value: payload?.postcode,
+      errorMessage: postcodeError && { text: postcodeError.message }
+    }
+  }
+}
+
+export const stepSchema = Joi.string()
+  .valid(...Object.keys(steps))
+  .required()
+
+const sharedPayloadSchemaKeys = {
+  crumb: crumbSchema,
+  step: stepSchema
+}
+
+/**
+ * Postcode lookup details form payload schema
+ * @type {ObjectSchema<PostcodeLookupDetailsPayload>}
+ */
+export const detailsPayloadSchema = Joi.object()
+  .keys({
+    ...sharedPayloadSchemaKeys,
+    [postcodeQueryFieldName]: Joi.string()
+      .pattern(/^[a-zA-Z]{1,2}\d[a-zA-Z\d]?\s?\d[a-zA-Z]{2}$/)
+      .trim()
+      .required()
+      .messages({
+        'string.pattern.base':
+          'Enter a valid postcode or enter an address manually',
+        '*': 'Enter a postcode'
+      }),
+    [buildingNameQueryFieldName]: Joi.string()
+      .trim()
+      .required()
+      .allow('')
+      .trim()
+  })
+  .required()
+
+/**
+ * Postcode lookup select form payload schema
+ * @type {ObjectSchema<PostcodeLookupSelectPayload>}
+ */
+export const selectPayloadSchema = Joi.object()
+  .keys({
+    ...sharedPayloadSchemaKeys,
+    [uprnFieldName]: Joi.string().required().messages({
+      '*': selectLabelText
+    })
+  })
+  .required()
+
+/**
+ * Postcode lookup manual form payload schema
+ * @type {ObjectSchema<PostcodeLookupManualPayload>}
+ */
+export const manualPayloadSchema = Joi.object()
+  .keys({
+    ...sharedPayloadSchemaKeys,
+    [line1FieldName]: Joi.string().trim().required().messages({
+      '*': 'Enter address line 1'
+    }),
+    [line2FieldName]: Joi.string().trim().allow('').required(),
+    [townFieldName]: Joi.string().trim().required().messages({
+      '*': 'Enter town or city'
+    }),
+    [countyFieldName]: Joi.string().trim().allow('').required(),
+    [postcodeFieldName]: Joi.string().trim().required().messages({
+      '*': 'Enter postcode'
+    })
+  })
+  .required()
+
+/**
+ * Get the postcode lookup href
+ * @param {string} [step] - the postcode lookup step
+ */
+function getHref(step) {
+  const query = step ? `?step=${step}` : ''
+
+  return `${JOURNEY_BASE_URL}${query}`
+}
+
+/**
+ * The postcode lookup details form view model
+ * @param {PostcodeLookupSessionData} data
+ * @param {PostcodeLookupDetailsData} [payload]
+ * @param {Error} [err]
+ */
+export function detailsViewModel(data, payload, err) {
+  const { componentTitle: pageTitle, formName, sourceUrl } = data.initial
+
+  const backLink = {
+    href: sourceUrl
+  }
+
+  const { errors, postcodeQueryError, buildingNameQueryError } =
+    buildErrors(err)
+
+  // Model fields
+  const fields = getDetailsFields(
+    payload ?? data.details,
+    postcodeQueryError,
+    buildingNameQueryError
+  )
+
+  // Model buttons
+  const continueButton = {
+    text: 'Find address',
+    classes: GOVUK_MARGIN_RIGHT_1
+  }
+  const manualLink = {
+    text: 'enter address manually',
+    href: getHref(steps.manual)
+  }
+
+  return {
+    step: steps.details,
+    showTitle: true,
+    name: formName,
+    serviceUrl: sourceUrl,
+    pageTitle,
+    backLink,
+    errors,
+    fields,
+    buttons: { continueButton, manualLink }
+  }
+}
+
+/**
+ * The postcode lookup select form view model
+ * @param {{ session: PostcodeLookupSessionData, apiKey: string }} data
+ * @param {PostcodeLookupSelectPayload} [payload]
+ * @param {Error} [err]
+ */
+export async function selectViewModel(data, payload, err) {
+  const { session, apiKey } = data
+  const { details, initial } = session
+  const { postcodeQuery, buildingNameQuery } = details
+
+  // Search for addresses
+  const {
+    hasAddresses,
+    hasMultipleAddresses,
+    singleAddress,
+    addresses,
+    addressCount
+  } = await getAddresses(postcodeQuery, buildingNameQuery, apiKey)
+
+  const title = hasAddresses ? initial.componentTitle : 'No address found'
+  const formPath = initial.sourceUrl
+  const href = getHref()
+
+  const backLink = { href }
+
+  const { errors, uprnError } = buildErrors(err)
+
+  // Model fields
+  const fields = getSelectFields(
+    details,
+    hasMultipleAddresses,
+    singleAddress,
+    payload,
+    uprnError,
+    addresses
+  )
+
+  const searchAgainLink = {
+    text: 'Search again',
+    href
+  }
+
+  // Model buttons
+  const continueButton = {
+    href: hasAddresses ? undefined : href,
+    text: hasAddresses ? 'Use this address' : 'Search again',
+    classes: GOVUK_MARGIN_RIGHT_1
+  }
+  const manualLink = {
+    text: 'enter address manually',
+    href: `${href}?step=${steps.manual}`
+  }
+
+  return {
+    step: steps.select,
+    showTitle: true,
+    name: title,
+    serviceUrl: formPath,
+    pageTitle: title,
+    backLink,
+    errors,
+    searchAgainLink,
+    fields,
+    details,
+    addressCount,
+    singleAddress,
+    hasAddresses,
+    hasMultipleAddresses,
+    buttons: { continueButton, manualLink }
+  }
+}
+
+/**
+ * The postcode lookup manual form view model
+ * @param {PostcodeLookupSessionData} data
+ * @param {PostcodeLookupManualPayload} [payload]
+ * @param {Error} [err]
+ */
+export function manualViewModel(data, payload, err) {
+  const { componentTitle, sourceUrl, componentHint } = data.initial
+  const formPath = sourceUrl
+  const href = getHref()
+
+  const backLink = {
+    href
+  }
+
+  const {
+    errors,
+    line1Error,
+    line2Error,
+    townError,
+    countyError,
+    postcodeError
+  } = buildErrors(err)
+
+  // Model hint
+  const hint = componentHint && {
+    text: componentHint
+  }
+
+  // Model fields
+  const fields = getManualFields(
+    payload,
+    line1Error,
+    line2Error,
+    townError,
+    countyError,
+    postcodeError
+  )
+
+  // Model buttons
+  const continueButton = {
+    text: 'Use this address',
+    classes: GOVUK_MARGIN_RIGHT_1
+  }
+  const detailsLink = {
+    text: 'find an address instead',
+    href
+  }
+
+  return {
+    step: steps.manual,
+    showTitle: true,
+    name: componentTitle,
+    serviceUrl: formPath,
+    pageTitle: componentTitle,
+    backLink,
+    errors,
+    hint,
+    fields,
+    buttons: { continueButton, detailsLink }
+  }
+}
+
+/** @typedef { ValidationErrorItem | undefined } OptionalValidationErrorItem */
+
+/**
+ * @import { ObjectSchema, ValidationErrorItem } from 'joi'
+ * @import { Address, PostcodeLookupDetailsData, PostcodeLookupDetailsPayload, PostcodeLookupManualPayload, PostcodeLookupSelectPayload, PostcodeLookupSessionData } from '~/src/server/plugins/postcode-lookup/types.js'
+ */
diff --git a/src/server/plugins/postcode-lookup/routes/index.js b/src/server/plugins/postcode-lookup/routes/index.js
new file mode 100644
index 000000000..7252e5fec
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/routes/index.js
@@ -0,0 +1,258 @@
+import Boom from '@hapi/boom'
+import { StatusCodes } from 'http-status-codes'
+import Joi from 'joi'
+
+import { EXTERNAL_STATE_APPENDAGE } from '~/src/server/constants.js'
+import {
+  JOURNEY_BASE_URL,
+  detailsPayloadSchema,
+  detailsViewModel,
+  manualPayloadSchema,
+  manualViewModel,
+  selectPayloadSchema,
+  selectViewModel,
+  stepSchema,
+  steps
+} from '~/src/server/plugins/postcode-lookup/models/index.js'
+import * as service from '~/src/server/plugins/postcode-lookup/service.js'
+
+const viewName = 'postcode-lookup-details'
+
+/**
+ * Get the session state associated with this journey
+ * @param {PostcodeLookupRequest} request
+ */
+function getSessionState(request) {
+  /**
+   * @type {PostcodeLookupSessionData | undefined}
+   */
+  const state = request.yar.get(JOURNEY_BASE_URL)
+
+  if (!state) {
+    throw Boom.internal(`No postcode lookup data found for ${JOURNEY_BASE_URL}`)
+  }
+
+  return state
+}
+
+/**
+ * Flash form component state
+ * @param {PostcodeLookupRequest} request - the request
+ * @param {string} componentName - the component name
+ * @param {Address | PostcodeLookupManualPayload} address - the address from ordnance survey or manually entered
+ */
+function flashComponentState(request, componentName, address) {
+  const addressState = {
+    addressLine1: address.addressLine1,
+    addressLine2: address.addressLine2,
+    town: address.town,
+    county: address.county,
+    postcode: address.postcode,
+    uprn: 'uprn' in address && address.uprn ? address.uprn : undefined
+  }
+
+  /**
+   * @type {ExternalStateAppendage}
+   */
+  const appendage = {
+    component: componentName,
+    data: addressState
+  }
+
+  request.yar.flash(EXTERNAL_STATE_APPENDAGE, appendage, true)
+}
+
+/**
+ * Initialises and dispatches the request to the postcode lookup journey
+ * @param {FormRequestPayload} request - the source page
+ * @param {FormResponseToolkit} h - the source page
+ * @param {PostcodeLookupDispatchData} initial - the source data
+ */
+export function dispatch(request, h, initial) {
+  /**
+   * @type {PostcodeLookupSessionData}
+   */
+  const data = {
+    initial,
+    details: { postcodeQuery: '', buildingNameQuery: '' }
+  }
+
+  request.yar.set(JOURNEY_BASE_URL, data)
+
+  const query = initial.step ? `?step=${initial.step}` : ''
+
+  return h.redirect(`${JOURNEY_BASE_URL}${query}`).code(StatusCodes.SEE_OTHER)
+}
+
+/**
+ * Gets the postcode lookup routes
+ * @param {PostcodeLookupConfiguration} options - ordnance survey api key
+ */
+export function getRoutes(options) {
+  return [getRoute(), postRoute(options)]
+}
+
+/**
+ * @returns {ServerRoute<PostcodeLookupGetRequestRefs>}
+ */
+function getRoute() {
+  return {
+    method: 'GET',
+    path: JOURNEY_BASE_URL,
+    handler(request, h) {
+      const { query } = request
+      const { step } = query
+      const session = getSessionState(request)
+
+      const model =
+        step === steps.manual
+          ? manualViewModel(session)
+          : detailsViewModel(session)
+
+      return h.view(viewName, model)
+    },
+    options: {
+      validate: {
+        query: Joi.object()
+          .keys({
+            step: Joi.string().allow(steps.details, steps.manual).optional()
+          })
+          .optional()
+      }
+    }
+  }
+}
+
+/**
+ * @param {PostcodeLookupConfiguration} options
+ * @returns {ServerRoute<PostcodeLookupPostRequestRefs>}
+ */
+function postRoute(options) {
+  return {
+    method: 'POST',
+    path: JOURNEY_BASE_URL,
+    async handler(request, h) {
+      const { payload } = request
+      const { step } = payload
+
+      switch (step) {
+        case steps.details: {
+          return detailsPostHandler(request, h, options)
+        }
+        case steps.select: {
+          return selectPostHandler(request, h, options)
+        }
+        case steps.manual: {
+          return manualPostHandler(request, h)
+        }
+        default:
+          throw Boom.badRequest(`Invalid step ${step}`)
+      }
+    },
+    options: {
+      validate: {
+        payload: Joi.object()
+          .keys({
+            step: stepSchema
+          })
+          .unknown(true)
+      }
+    }
+  }
+}
+
+/**
+ * Post handler for the details step
+ * @param {PostcodeLookupPostRequest} request
+ * @param {ResponseToolkit<PostcodeLookupPostRequestRefs>} h
+ * @param {PostcodeLookupConfiguration} options
+ */
+async function detailsPostHandler(request, h, options) {
+  const { payload } = request
+  const session = getSessionState(request)
+  const { ordnanceSurveyApiKey: apiKey } = options
+  const { value: details, error } = detailsPayloadSchema.validate(payload)
+
+  let model
+
+  if (error) {
+    model = detailsViewModel(session, details, error)
+
+    return h.view(viewName, model)
+  }
+
+  const { postcodeQuery, buildingNameQuery } = details
+  session.details = { postcodeQuery, buildingNameQuery }
+
+  // Store the updated session
+  request.yar.set(JOURNEY_BASE_URL, session)
+
+  model = await selectViewModel({ session, apiKey })
+
+  return h.view(viewName, model)
+}
+
+/**
+ * Post handler for the select step
+ * @param {PostcodeLookupPostRequest} request
+ * @param {ResponseToolkit<PostcodeLookupPostRequestRefs>} h
+ * @param {PostcodeLookupConfiguration} options
+ */
+async function selectPostHandler(request, h, options) {
+  const { payload } = request
+  const session = getSessionState(request)
+  const { ordnanceSurveyApiKey: apiKey } = options
+  const { value: select, error } = selectPayloadSchema.validate(payload)
+
+  if (error) {
+    const model = await selectViewModel({ session, apiKey }, select, error)
+
+    return h.view(viewName, model)
+  }
+
+  const addresses = await service.searchByUPRN(select.uprn, apiKey)
+  const property = addresses.at(0)
+
+  if (!property) {
+    throw Boom.internal(`UPRN ${property} not found`)
+  }
+
+  const { componentName, sourceUrl } = session.initial
+  flashComponentState(request, componentName, property)
+
+  // Redirect back to the source form page
+  return h.redirect(sourceUrl).code(StatusCodes.SEE_OTHER)
+}
+
+/**
+ * Post handler for the manual step
+ * @param {PostcodeLookupPostRequest} request
+ * @param {ResponseToolkit<PostcodeLookupPostRequestRefs>} h
+ */
+function manualPostHandler(request, h) {
+  const { payload } = request
+  const session = getSessionState(request)
+
+  const { value: manual, error } = manualPayloadSchema.validate(payload, {
+    abortEarly: false
+  })
+
+  if (error) {
+    const model = manualViewModel(session, manual, error)
+
+    return h.view(viewName, model)
+  }
+
+  const { componentName, sourceUrl } = session.initial
+  flashComponentState(request, componentName, manual)
+
+  // Redirect back to the source form page
+  return h.redirect(sourceUrl).code(StatusCodes.SEE_OTHER)
+}
+
+/**
+ * @import { ResponseToolkit, ServerRoute } from '@hapi/hapi'
+ * @import { PostcodeLookupManualPayload, Address, PostcodeLookupGetRequestRefs, PostcodeLookupPostRequestRefs, PostcodeLookupRequest, PostcodeLookupPostRequest, PostcodeLookupConfiguration, PostcodeLookupDispatchData, PostcodeLookupSessionData } from '~/src/server/plugins/postcode-lookup/types.js'
+ * @import { FormRequestPayload, FormResponseToolkit } from '~/src/server/routes/types.js'
+ * @import { ExternalStateAppendage } from '~/src/server/plugins/engine/types.js'
+ */
diff --git a/src/server/plugins/postcode-lookup/service.js b/src/server/plugins/postcode-lookup/service.js
new file mode 100644
index 000000000..d8614bcd1
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/service.js
@@ -0,0 +1,188 @@
+import { getErrorMessage } from '@defra/forms-model'
+import Boom from '@hapi/boom'
+
+import { createLogger } from '~/src/server/common/helpers/logging/logger.js'
+import { getJson } from '~/src/server/services/httpService.js'
+
+const logger = createLogger()
+
+/**
+ * Returns an empty result set
+ */
+function empty() {
+  return []
+}
+
+/**
+ * Logs OS places errors
+ * @param {unknown} err - the error
+ * @param {string} endpoint - the OS api endpoint
+ */
+function logErrorAndReturnEmpty(err, endpoint) {
+  const msg = `${getErrorMessage(err)} ${(Boom.isBoom(err) && err.data?.payload?.error?.message) ?? ''}`
+
+  logger.error(err, `Exception occured calling OS places ${endpoint} - ${msg}}`)
+
+  return empty()
+}
+
+/**
+ * Fetch data from OS API
+ * @param {string} url - the url to get address json data from
+ * @param {string} endpoint - the url endpoint description for logging
+ */
+async function getAddressData(url, endpoint) {
+  const getJsonByType =
+    /** @type {typeof getJson<DeliveryPointAddressResult>} */ (getJson)
+
+  try {
+    const response = await getJsonByType(url)
+
+    if (response.error) {
+      return logErrorAndReturnEmpty(response.error, endpoint)
+    }
+
+    const results = response.payload.results
+
+    if (!Array.isArray(results)) {
+      return empty()
+    }
+
+    return results.map((result) => formatAddress(result.DPA))
+  } catch (err) {
+    return logErrorAndReturnEmpty(err, endpoint)
+  }
+}
+
+/**
+ * OS places search
+ * @param {string} query - the search term
+ * @param {string} apiKey - the OS api key
+ */
+export async function searchByQuery(query, apiKey) {
+  const endpoint = 'find'
+  const url = `https://api.os.uk/search/places/v1/${endpoint}?query=${encodeURIComponent(query)}&key=${apiKey}`
+
+  return getAddressData(url, endpoint)
+}
+
+/**
+ * OS postcode search
+ * @param {string} postcode - the postcode
+ * @param {string} apiKey - the OS api key
+ */
+export async function searchByPostcode(postcode, apiKey) {
+  const endpoint = 'postcode'
+  const url = `https://api.os.uk/search/places/v1/${endpoint}?postcode=${encodeURIComponent(postcode.replaceAll(/\s/g, ''))}&key=${apiKey}`
+
+  return getAddressData(url, endpoint)
+}
+
+/**
+ * OS UPRN search
+ * @param {string} uprn - the unique property reference number
+ * @param {string} apiKey - the OS api key
+ */
+export async function searchByUPRN(uprn, apiKey) {
+  const endpoint = 'uprn'
+  const url = `https://api.os.uk/search/places/v1/${endpoint}?uprn=${uprn}&key=${apiKey}`
+
+  return getAddressData(url, endpoint)
+}
+
+/**
+ * OS postcode and building name search
+ * @param {string} postcodeQuery - the postcode query
+ * @param {string} buildingNameQuery - the building name query
+ * @param {string} apiKey - the OS api key
+ */
+export async function search(postcodeQuery, buildingNameQuery, apiKey) {
+  let addresses = await searchByPostcode(postcodeQuery, apiKey)
+
+  if (buildingNameQuery) {
+    addresses = addresses.filter((item) =>
+      item.address.includes(buildingNameQuery.toUpperCase())
+    )
+  }
+
+  return addresses
+}
+
+/**
+ * Converts a delivery point address to an address
+ * Taken from http://github.com/dwp/find-an-address-plugin/blob/main/utils/getData.js
+ * @param {DeliveryPointAddress} dpa
+ */
+function formatAddress(dpa) {
+  const addressLine1 = formatAddressLine1(dpa)
+  const addressLine2 = formatAddressLine2(dpa)
+  const town = titleCase(dpa.POST_TOWN || '')
+  const postcode = dpa.POSTCODE || ''
+  const lines = [addressLine1, addressLine2, town]
+  const formatted = `${lines.filter((i) => !!i).join(', ')}, ${postcode}`
+
+  /**
+   * @type {Address}
+   */
+  const address = {
+    uprn: dpa.UPRN,
+    address: dpa.ADDRESS,
+    addressLine1,
+    addressLine2,
+    town,
+    county: '',
+    postcode,
+    formatted
+  }
+
+  return address
+}
+
+/**
+ * @param {DeliveryPointAddress} dpa
+ */
+function formatAddressLine1(dpa) {
+  return titleCase(
+    dpa.ORGANISATION_NAME ||
+      dpa.SUB_BUILDING_NAME ||
+      dpa.BUILDING_NAME ||
+      dpa.BUILDING_NUMBER
+      ? [
+          dpa.ORGANISATION_NAME || '',
+          dpa.SUB_BUILDING_NAME || '',
+          dpa.BUILDING_NAME || '',
+          dpa.BUILDING_NUMBER || ''
+        ]
+          .filter((item) => !!item)
+          .join(' ')
+      : ''
+  )
+}
+
+/**
+ * @param {DeliveryPointAddress} dpa
+ */
+function formatAddressLine2(dpa) {
+  return titleCase(
+    dpa.THOROUGHFARE_NAME || dpa.DEPENDENT_LOCALITY
+      ? [dpa.THOROUGHFARE_NAME || '', dpa.DEPENDENT_LOCALITY || '']
+          .filter((item) => !!item)
+          .join(', ')
+      : ''
+  )
+}
+
+/**
+ * Title case address
+ * @param {string} address
+ */
+function titleCase(address) {
+  return address
+    .split(' ')
+    .map((item) => item.charAt(0).toUpperCase() + item.slice(1).toLowerCase())
+    .join(' ')
+}
+
+/**
+ * @import { Address, DeliveryPointAddress, DeliveryPointAddressResult } from '~/src/server/plugins/postcode-lookup/types.js'
+ */
diff --git a/src/server/plugins/postcode-lookup/service.test.js b/src/server/plugins/postcode-lookup/service.test.js
new file mode 100644
index 000000000..57f301385
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/service.test.js
@@ -0,0 +1,177 @@
+import Boom from '@hapi/boom'
+
+import * as service from '~/src/server/plugins/postcode-lookup/service.js'
+import { result as postcodeResult } from '~/src/server/plugins/postcode-lookup/test/__stubs__/postcode.js'
+import { result as queryResult } from '~/src/server/plugins/postcode-lookup/test/__stubs__/query.js'
+import { result as uprnResult } from '~/src/server/plugins/postcode-lookup/test/__stubs__/uprn.js'
+import { getJson } from '~/src/server/services/httpService.js'
+
+jest.mock('~/src/server/services/httpService.ts')
+
+describe('Postcode lookup service', () => {
+  describe('searchByPostcode', () => {
+    it('should return formatted addresses', async () => {
+      jest.mocked(getJson).mockResolvedValueOnce({
+        res: /** @type {IncomingMessage} */ ({
+          statusCode: 200,
+          headers: {}
+        }),
+        payload: postcodeResult,
+        error: undefined
+      })
+
+      const results = await service.searchByPostcode('NW1 6XE', 'apikey')
+
+      expect(results).toHaveLength(10)
+      expect(results.at(0)).toEqual({
+        address: "EMILIA'S CRAFTED PASTA, 215, BAKER STREET, LONDON, NW1 6XE",
+        addressLine1: "Emilia's Crafted Pasta 215",
+        addressLine2: 'Baker Street',
+        county: '',
+        formatted: "Emilia's Crafted Pasta 215, Baker Street, London, NW1 6XE",
+        postcode: 'NW1 6XE',
+        town: 'London',
+        uprn: '10033619968'
+      })
+    })
+
+    it('should return an empty response when an error is encountered', async () => {
+      jest.mocked(getJson).mockResolvedValueOnce({
+        res: /** @type {IncomingMessage} */ ({
+          statusCode: 300,
+          headers: {}
+        }),
+        payload: undefined,
+        error: new Error('Unknown error')
+      })
+
+      const results = await service.searchByPostcode('NW1 6XE', 'apikey')
+
+      expect(results).toHaveLength(0)
+      expect(results).toEqual([])
+    })
+
+    it('should return an empty response when a non 200 response is encountered', async () => {
+      jest
+        .mocked(getJson)
+        .mockRejectedValueOnce(
+          Boom.badRequest(
+            'OS API error',
+            new Error('Invalid postcode segments')
+          )
+        )
+
+      const results = await service.searchByPostcode(
+        'invalid postcode',
+        'apikey'
+      )
+
+      expect(results).toHaveLength(0)
+      expect(results).toEqual([])
+    })
+
+    it('should return an empty response when no results are returned', async () => {
+      jest.mocked(getJson).mockResolvedValueOnce({
+        res: /** @type {IncomingMessage} */ ({
+          statusCode: 200,
+          headers: {}
+        }),
+        payload: { results: undefined },
+        error: undefined
+      })
+
+      const results = await service.searchByPostcode('NW1 6XE', 'apikey')
+
+      expect(results).toHaveLength(0)
+      expect(results).toEqual([])
+    })
+  })
+
+  describe('searchByUPRN', () => {
+    it('should return formatted addresses', async () => {
+      jest.mocked(getJson).mockResolvedValueOnce({
+        res: /** @type {IncomingMessage} */ ({
+          statusCode: 200,
+          headers: {}
+        }),
+        payload: uprnResult,
+        error: undefined
+      })
+
+      const results = await service.searchByUPRN('100023071949', 'apikey')
+
+      expect(results).toHaveLength(1)
+      expect(results.at(0)).toEqual({
+        address: 'SHERLOCK HOLMES MUSEUM, 221B, BAKER STREET, LONDON, NW1 6XE',
+        addressLine1: 'Sherlock Holmes Museum 221b',
+        addressLine2: 'Baker Street',
+        county: '',
+        formatted: 'Sherlock Holmes Museum 221b, Baker Street, London, NW1 6XE',
+        postcode: 'NW1 6XE',
+        town: 'London',
+        uprn: '100023071949'
+      })
+    })
+  })
+
+  describe('searchByQuery', () => {
+    it('should return formatted addresses', async () => {
+      jest.mocked(getJson).mockResolvedValueOnce({
+        res: /** @type {IncomingMessage} */ ({
+          statusCode: 200,
+          headers: {}
+        }),
+        payload: queryResult,
+        error: undefined
+      })
+
+      const results = await service.searchByQuery(
+        'Prime minister downing',
+        'apikey'
+      )
+
+      expect(results).toHaveLength(5)
+      expect(results.at(0)).toEqual({
+        address: 'BAKER STREET COTTAGE, BAKER STREET, FROME, BA11 3BL',
+        addressLine1: 'Baker Street Cottage',
+        addressLine2: 'Baker Street',
+        town: 'Frome',
+        county: '',
+        formatted: 'Baker Street Cottage, Baker Street, Frome, BA11 3BL',
+        postcode: 'BA11 3BL',
+        uprn: '250034655'
+      })
+    })
+  })
+
+  describe('search', () => {
+    it('should return formatted addresses', async () => {
+      jest.mocked(getJson).mockResolvedValueOnce({
+        res: /** @type {IncomingMessage} */ ({
+          statusCode: 200,
+          headers: {}
+        }),
+        payload: postcodeResult,
+        error: undefined
+      })
+
+      const results = await service.search('NW1 6XE', 'Emilia', 'apikey')
+
+      expect(results).toHaveLength(1)
+      expect(results.at(0)).toEqual({
+        address: "EMILIA'S CRAFTED PASTA, 215, BAKER STREET, LONDON, NW1 6XE",
+        addressLine1: "Emilia's Crafted Pasta 215",
+        addressLine2: 'Baker Street',
+        county: '',
+        formatted: "Emilia's Crafted Pasta 215, Baker Street, London, NW1 6XE",
+        postcode: 'NW1 6XE',
+        town: 'London',
+        uprn: '10033619968'
+      })
+    })
+  })
+})
+
+/**
+ * @import  { IncomingMessage } from 'node:http'
+ */
diff --git a/src/server/plugins/postcode-lookup/test/__stubs__/postcode.js b/src/server/plugins/postcode-lookup/test/__stubs__/postcode.js
new file mode 100644
index 000000000..bcbcc3a92
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/test/__stubs__/postcode.js
@@ -0,0 +1,382 @@
+export const result = {
+  header: {
+    uri: 'https://api.os.uk/search/places/v1/postcode?postcode=NW1%206XE',
+    query: 'postcode=NW1 6XE',
+    offset: 0,
+    totalresults: 10,
+    format: 'JSON',
+    dataset: 'DPA',
+    lr: 'EN,CY',
+    maxresults: 100,
+    epoch: '121',
+    lastupdate: '2025-10-14',
+    output_srs: 'EPSG:27700'
+  },
+  results: [
+    {
+      DPA: {
+        UPRN: '10033619968',
+        UDPRN: '50825076',
+        ADDRESS: "EMILIA'S CRAFTED PASTA, 215, BAKER STREET, LONDON, NW1 6XE",
+        ORGANISATION_NAME: "EMILIA'S CRAFTED PASTA",
+        BUILDING_NUMBER: '215',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '2',
+        X_COORDINATE: 527870.4,
+        Y_COORDINATE: 182081.17,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CR07',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Restaurant / Cafeteria',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158430',
+        WARD_CODE: 'E05013805',
+        PARENT_UPRN: '10033659670',
+        LAST_UPDATE_DATE: '20/01/2025',
+        ENTRY_DATE: '13/02/2013',
+        BLPU_STATE_DATE: '13/02/2013',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1H'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033619969',
+        UDPRN: '50825094',
+        ADDRESS: 'FLAT 1-86, 219, BAKER STREET, LONDON, NW1 6XE',
+        SUB_BUILDING_NAME: 'FLAT 1-86',
+        BUILDING_NUMBER: '219',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527868.08,
+        Y_COORDINATE: 182090.78,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'PP',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Property Shell',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158430',
+        WARD_CODE: 'E05013805',
+        PARENT_UPRN: '10033659670',
+        LAST_UPDATE_DATE: '20/01/2025',
+        ENTRY_DATE: '13/02/2013',
+        BLPU_STATE_DATE: '13/02/2013',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '7J'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033625299',
+        UDPRN: '54761212',
+        ADDRESS:
+          'PARKVIEW ESTATES MANAGEMENT LTD, 219, BAKER STREET, LONDON, NW1 6XE',
+        ORGANISATION_NAME: 'PARKVIEW ESTATES MANAGEMENT LTD',
+        BUILDING_NUMBER: '219',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527868.08,
+        Y_COORDINATE: 182090.78,
+        STATUS: 'HISTORICAL',
+        LOGICAL_STATUS_CODE: '8',
+        CLASSIFICATION_CODE: 'CL06',
+        CLASSIFICATION_CODE_DESCRIPTION:
+          'Indoor / Outdoor Leisure / Sporting Activity / Centre',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '4',
+        BLPU_STATE_CODE_DESCRIPTION: 'No longer existing',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158430',
+        WARD_CODE: 'E05013805',
+        LAST_UPDATE_DATE: '22/02/2024',
+        ENTRY_DATE: '20/10/2014',
+        BLPU_STATE_DATE: '25/11/2022',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1G'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '100022723861',
+        UDPRN: '17646245',
+        ADDRESS: '235, BAKER STREET, LONDON, NW1 6XE',
+        BUILDING_NUMBER: '235',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527850.0,
+        Y_COORDINATE: 182134.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'PP',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Property Shell',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158434',
+        WARD_CODE: 'E05013805',
+        LAST_UPDATE_DATE: '10/02/2016',
+        ENTRY_DATE: '19/03/2001',
+        BLPU_STATE_DATE: '19/03/2001',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '2H'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '100023072608',
+        UDPRN: '17646236',
+        ADDRESS: '237, BAKER STREET, LONDON, NW1 6XE',
+        BUILDING_NUMBER: '237',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527850.0,
+        Y_COORDINATE: 182139.0,
+        STATUS: 'HISTORICAL',
+        LOGICAL_STATUS_CODE: '8',
+        CLASSIFICATION_CODE: 'CR08',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Shop / Showroom',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '4',
+        BLPU_STATE_CODE_DESCRIPTION: 'No longer existing',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158435',
+        WARD_CODE: 'E05013805',
+        LAST_UPDATE_DATE: '22/02/2024',
+        ENTRY_DATE: '19/03/2001',
+        BLPU_STATE_DATE: '01/10/2013',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '2G'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '100023071949',
+        UDPRN: '17646242',
+        ADDRESS: 'SHERLOCK HOLMES MUSEUM, 221B, BAKER STREET, LONDON, NW1 6XE',
+        ORGANISATION_NAME: 'SHERLOCK HOLMES MUSEUM',
+        BUILDING_NAME: '221B',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '2',
+        X_COORDINATE: 527847.0,
+        Y_COORDINATE: 182144.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CR08',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Shop / Showroom',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158436',
+        WARD_CODE: 'E05013805',
+        LAST_UPDATE_DATE: '23/09/2018',
+        ENTRY_DATE: '19/03/2001',
+        BLPU_STATE_DATE: '19/03/2001',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1F'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033605426',
+        UDPRN: '17646231',
+        ADDRESS: 'LONDON BEATLES STORE, 231-233, BAKER STREET, LONDON, NW1 6XE',
+        ORGANISATION_NAME: 'LONDON BEATLES STORE',
+        BUILDING_NAME: '231-233',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527854.0,
+        Y_COORDINATE: 182123.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CR08',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Shop / Showroom',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158432',
+        WARD_CODE: 'E05013805',
+        PARENT_UPRN: '100023072617',
+        LAST_UPDATE_DATE: '10/02/2016',
+        ENTRY_DATE: '25/02/2009',
+        BLPU_STATE_DATE: '25/02/2009',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1A'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033529292',
+        UDPRN: '17646238',
+        ADDRESS: 'TOTAL CHI, 241-243, BAKER STREET, LONDON, NW1 6XE',
+        ORGANISATION_NAME: 'TOTAL CHI',
+        BUILDING_NAME: '241-243',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '2',
+        X_COORDINATE: 527844.0,
+        Y_COORDINATE: 182155.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CR08',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Shop / Showroom',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158438',
+        WARD_CODE: 'E05013805',
+        PARENT_UPRN: '100023071621',
+        LAST_UPDATE_DATE: '23/09/2018',
+        ENTRY_DATE: '27/04/2003',
+        BLPU_STATE_DATE: '27/04/2003',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1B'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033529295',
+        UDPRN: '52154612',
+        ADDRESS: 'FLAT 1-5, 245-247, BAKER STREET, LONDON, NW1 6XE',
+        SUB_BUILDING_NAME: 'FLAT 1-5',
+        BUILDING_NAME: '245-247',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527839.0,
+        Y_COORDINATE: 182163.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'PP',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Property Shell',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158439',
+        WARD_CODE: 'E05013805',
+        LAST_UPDATE_DATE: '10/02/2016',
+        ENTRY_DATE: '27/04/2003',
+        BLPU_STATE_DATE: '27/04/2003',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1E'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033625010',
+        UDPRN: '17646244',
+        ADDRESS: 'THE VOLUNTEER, 245-247, BAKER STREET, LONDON, NW1 6XE',
+        ORGANISATION_NAME: 'THE VOLUNTEER',
+        BUILDING_NAME: '245-247',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '1',
+        X_COORDINATE: 527839.0,
+        Y_COORDINATE: 182163.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CR06',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Public House / Bar / Nightclub',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158439',
+        WARD_CODE: 'E05013805',
+        PARENT_UPRN: '10033529295',
+        LAST_UPDATE_DATE: '17/05/2019',
+        ENTRY_DATE: '02/10/2014',
+        BLPU_STATE_DATE: '02/10/2014',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1R'
+      }
+    }
+  ]
+}
diff --git a/src/server/plugins/postcode-lookup/test/__stubs__/query.js b/src/server/plugins/postcode-lookup/test/__stubs__/query.js
new file mode 100644
index 000000000..3fbfd2383
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/test/__stubs__/query.js
@@ -0,0 +1,200 @@
+export const result = {
+  header: {
+    uri: 'https://api.os.uk/search/places/v1/find?query=baker%20street',
+    query: 'query=baker street',
+    offset: 0,
+    totalresults: 10,
+    format: 'JSON',
+    dataset: 'DPA',
+    lr: 'EN,CY',
+    maxresults: 100,
+    matchprecision: 1,
+    epoch: '121',
+    lastupdate: '2025-10-14',
+    output_srs: 'EPSG:27700'
+  },
+  results: [
+    {
+      DPA: {
+        UPRN: '250034655',
+        UDPRN: '1216958',
+        ADDRESS: 'BAKER STREET COTTAGE, BAKER STREET, FROME, BA11 3BL',
+        BUILDING_NAME: 'BAKER STREET COTTAGE',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'FROME',
+        POSTCODE: 'BA11 3BL',
+        RPC: '1',
+        X_COORDINATE: 377184.0,
+        Y_COORDINATE: 148060.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'RD04',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Terraced',
+        LOCAL_CUSTODIAN_CODE: 3300,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'SOMERSET',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000015533989',
+        WARD_CODE: 'E05014362',
+        PARISH_CODE: 'E04008560',
+        LAST_UPDATE_DATE: '31/03/2023',
+        ENTRY_DATE: '29/03/2000',
+        BLPU_STATE_DATE: '29/03/2000',
+        LANGUAGE: 'EN',
+        MATCH: 0.4,
+        MATCH_DESCRIPTION: 'NO MATCH',
+        DELIVERY_POINT_SUFFIX: '1L'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033336368',
+        UDPRN: '52500297',
+        ADDRESS: 'BAKER STREET CINEMA, BAKER STREET, ABERGAVENNY, NP7 5BB',
+        ORGANISATION_NAME: 'BAKER STREET CINEMA',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'ABERGAVENNY',
+        POSTCODE: 'NP7 5BB',
+        RPC: '2',
+        X_COORDINATE: 329751.36,
+        Y_COORDINATE: 214353.3,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CL07CI',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Cinema',
+        LOCAL_CUSTODIAN_CODE: 6840,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'MONMOUTHSHIRE',
+        COUNTRY_CODE: 'W',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within Wales',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000021003409',
+        WARD_CODE: 'W05001775',
+        PARISH_CODE: 'W04001057',
+        PARENT_UPRN: '10033345846',
+        LAST_UPDATE_DATE: '25/02/2025',
+        ENTRY_DATE: '11/11/2005',
+        BLPU_STATE_DATE: '07/07/2010',
+        LANGUAGE: 'EN',
+        MATCH: 0.4,
+        MATCH_DESCRIPTION: 'NO MATCH',
+        DELIVERY_POINT_SUFFIX: '2A'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '10033336368',
+        UDPRN: '52500297',
+        ADDRESS: 'BAKER STREET CINEMA, BAKER STREET, Y FENNI, NP7 5BB',
+        ORGANISATION_NAME: 'BAKER STREET CINEMA',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'Y FENNI',
+        POSTCODE: 'NP7 5BB',
+        RPC: '2',
+        X_COORDINATE: 329751.36,
+        Y_COORDINATE: 214353.3,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CL07CI',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Cinema',
+        LOCAL_CUSTODIAN_CODE: 6840,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'MONMOUTHSHIRE',
+        COUNTRY_CODE: 'W',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within Wales',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000021003409',
+        WARD_CODE: 'W05001775',
+        PARISH_CODE: 'W04001057',
+        PARENT_UPRN: '10033345846',
+        LAST_UPDATE_DATE: '25/02/2025',
+        ENTRY_DATE: '11/11/2005',
+        BLPU_STATE_DATE: '07/07/2010',
+        LANGUAGE: 'CY',
+        MATCH: 0.4,
+        MATCH_DESCRIPTION: 'NO MATCH',
+        DELIVERY_POINT_SUFFIX: '2A'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '100100269282',
+        UDPRN: '17105375',
+        ADDRESS: '6, BAKER STREET, Y FENNI, NP7 5BB',
+        BUILDING_NUMBER: '6',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'Y FENNI',
+        POSTCODE: 'NP7 5BB',
+        RPC: '2',
+        X_COORDINATE: 329754.0,
+        Y_COORDINATE: 214382.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'RD03',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Semi-Detached',
+        LOCAL_CUSTODIAN_CODE: 6840,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'MONMOUTHSHIRE',
+        COUNTRY_CODE: 'W',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within Wales',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000021003407',
+        WARD_CODE: 'W05001775',
+        PARISH_CODE: 'W04001057',
+        LAST_UPDATE_DATE: '17/10/2016',
+        ENTRY_DATE: '10/05/2001',
+        BLPU_STATE_DATE: '06/09/2016',
+        LANGUAGE: 'CY',
+        MATCH: 0.4,
+        MATCH_DESCRIPTION: 'NO MATCH',
+        DELIVERY_POINT_SUFFIX: '1L'
+      }
+    },
+    {
+      DPA: {
+        UPRN: '100100269283',
+        UDPRN: '17105376',
+        ADDRESS: '8, BAKER STREET, Y FENNI, NP7 5BB',
+        BUILDING_NUMBER: '8',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'Y FENNI',
+        POSTCODE: 'NP7 5BB',
+        RPC: '1',
+        X_COORDINATE: 329753.0,
+        Y_COORDINATE: 214380.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'RD03',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Semi-Detached',
+        LOCAL_CUSTODIAN_CODE: 6840,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'MONMOUTHSHIRE',
+        COUNTRY_CODE: 'W',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within Wales',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000021003408',
+        WARD_CODE: 'W05001775',
+        PARISH_CODE: 'W04001057',
+        LAST_UPDATE_DATE: '17/10/2016',
+        ENTRY_DATE: '10/05/2001',
+        BLPU_STATE_DATE: '06/09/2016',
+        LANGUAGE: 'CY',
+        MATCH: 0.4,
+        MATCH_DESCRIPTION: 'NO MATCH',
+        DELIVERY_POINT_SUFFIX: '1N'
+      }
+    }
+  ]
+}
diff --git a/src/server/plugins/postcode-lookup/test/__stubs__/uprn.js b/src/server/plugins/postcode-lookup/test/__stubs__/uprn.js
new file mode 100644
index 000000000..32893812a
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/test/__stubs__/uprn.js
@@ -0,0 +1,53 @@
+export const result = {
+  header: {
+    uri: 'https://api.os.uk/search/places/v1/uprn?uprn=100023071949',
+    query: 'uprn=100023071949',
+    offset: 0,
+    totalresults: 1,
+    format: 'JSON',
+    dataset: 'DPA',
+    lr: 'EN,CY',
+    maxresults: 100,
+    epoch: '121',
+    lastupdate: '2025-10-14',
+    output_srs: 'EPSG:27700'
+  },
+  results: [
+    {
+      DPA: {
+        UPRN: '100023071949',
+        UDPRN: '17646242',
+        ADDRESS: 'SHERLOCK HOLMES MUSEUM, 221B, BAKER STREET, LONDON, NW1 6XE',
+        ORGANISATION_NAME: 'SHERLOCK HOLMES MUSEUM',
+        BUILDING_NAME: '221B',
+        THOROUGHFARE_NAME: 'BAKER STREET',
+        POST_TOWN: 'LONDON',
+        POSTCODE: 'NW1 6XE',
+        RPC: '2',
+        X_COORDINATE: 527847.0,
+        Y_COORDINATE: 182144.0,
+        STATUS: 'APPROVED',
+        LOGICAL_STATUS_CODE: '1',
+        CLASSIFICATION_CODE: 'CR08',
+        CLASSIFICATION_CODE_DESCRIPTION: 'Shop / Showroom',
+        LOCAL_CUSTODIAN_CODE: 5990,
+        LOCAL_CUSTODIAN_CODE_DESCRIPTION: 'CITY OF WESTMINSTER',
+        COUNTRY_CODE: 'E',
+        COUNTRY_CODE_DESCRIPTION: 'This record is within England',
+        POSTAL_ADDRESS_CODE: 'D',
+        POSTAL_ADDRESS_CODE_DESCRIPTION: 'A record which is linked to PAF',
+        BLPU_STATE_CODE: '2',
+        BLPU_STATE_CODE_DESCRIPTION: 'In use',
+        TOPOGRAPHY_LAYER_TOID: 'osgb1000005158436',
+        WARD_CODE: 'E05013805',
+        LAST_UPDATE_DATE: '23/09/2018',
+        ENTRY_DATE: '19/03/2001',
+        BLPU_STATE_DATE: '19/03/2001',
+        LANGUAGE: 'EN',
+        MATCH: 1.0,
+        MATCH_DESCRIPTION: 'EXACT',
+        DELIVERY_POINT_SUFFIX: '1F'
+      }
+    }
+  ]
+}
diff --git a/src/server/plugins/postcode-lookup/types.js b/src/server/plugins/postcode-lookup/types.js
new file mode 100644
index 000000000..49ca24a11
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/types.js
@@ -0,0 +1,143 @@
+/**
+ * @typedef {{
+ *   ordnanceSurveyApiKey: string
+ * }} PostcodeLookupConfiguration
+ */
+
+/**
+ * @typedef {{
+ *   name: string
+ *   step?: string
+ * }} PostcodeLookupDispatchArgs
+ */
+
+/**
+ * @typedef {{
+ *   sourceUrl: string,
+ *   formName: string
+ *   componentName: string
+ *   componentTitle: string,
+ *   componentHint?: string
+ *   step?: string
+ * }} PostcodeLookupDispatchData
+ */
+
+/**
+ * @typedef {{
+ *   initial: PostcodeLookupDispatchData
+ *   details: PostcodeLookupDetailsData
+ * }} PostcodeLookupSessionData
+ */
+
+//
+// Model types
+//
+
+/**
+ * The postcode lookup details form view model data
+ * @typedef {object} PostcodeLookupDetailsData
+ * @property {string} postcodeQuery - postcode query
+ * @property {string} buildingNameQuery - Building name or number query
+ */
+
+//
+// Route types
+//
+
+/**
+ * Postcode lookup query params
+ * @typedef {object} PostcodeLookupQuery
+ * @property {string} [step] - step
+ */
+
+/**
+ * @typedef {object} PostcodeLookupDetailsPayloadProperties
+ * @property {string} step - step
+ */
+
+/**
+ * @typedef {PostcodeLookupDetailsData & PostcodeLookupDetailsPayloadProperties} PostcodeLookupDetailsPayload
+ */
+
+/**
+ * @typedef {object} PostcodeLookupSelectPayload
+ * @property {string} step - step
+ * @property {string} uprn - postcode
+ */
+
+/**
+ * Postcode lookup get request
+ * @typedef {object} PostcodeLookupGetRequestRefs
+ * @property {PostcodeLookupQuery} Query - Request query
+ */
+
+/**
+ * Postcode lookup post request
+ * @typedef {object} PostcodeLookupPostRequestRefs
+ * @property {PostcodeLookupDetailsPayload | PostcodeLookupSelectPayload} Payload - Request payload
+ */
+
+/**
+ * @typedef {PostcodeLookupGetRequestRefs | PostcodeLookupPostRequestRefs} PostcodeLookupRequestRefs
+ * @typedef {Request<PostcodeLookupGetRequestRefs>} PostcodeLookupGetRequest
+ * @typedef {Request<PostcodeLookupPostRequestRefs>} PostcodeLookupPostRequest
+ * @typedef {PostcodeLookupGetRequest | PostcodeLookupPostRequest} PostcodeLookupRequest
+ */
+
+/**
+ * @typedef {object} PostcodeLookupManualPayload
+ * @property {string} addressLine1 - The address line 1
+ * @property {string} addressLine2 - The address line 2
+ * @property {string} town - The address town or city
+ * @property {string} county - The address county
+ * @property {string} postcode - The address postcode
+ */
+
+//
+// Service types
+//
+
+/**
+ * @typedef {object} Address
+ * @property {string} uprn - The unique property reference
+ * @property {string} address - The full address
+ * @property {string} addressLine1 - Address line 1
+ * @property {string} addressLine2 - Address line 2
+ * @property {string} town - Address town
+ * @property {string} county - Address county
+ * @property {string} postcode - Address postcode
+ * @property {string} formatted - The full formatted address
+ */
+
+/**
+ * OS places address response
+ * @typedef {object} DeliveryPointAddress
+ * @property {string} UPRN - Unique property reference number
+ * @property {string} UDPRN - Unique delivery point Reference Number
+ * @property {string} ADDRESS - Address
+ * @property {string} ORGANISATION_NAME - Organisation name
+ * @property {string} SUB_BUILDING_NAME - Sub building name
+ * @property {string} BUILDING_NAME - Building name
+ * @property {string} BUILDING_NUMBER - Building number
+ * @property {string} THOROUGHFARE_NAME - Throughfare name
+ * @property {string} DEPENDENT_LOCALITY - Dependent locality
+ * @property {string} POST_TOWN - Post town
+ * @property {string} POSTCODE - Postcode
+ */
+
+/**
+ * OS places DPA response
+ * @typedef {object} DeliveryPointAddressItem
+ * @property {DeliveryPointAddress} DPA - Delivery point address
+ */
+
+/**
+ * OS places DPA response
+ * @typedef {object} DeliveryPointAddressResult
+ * @property {DeliveryPointAddressItem[]} [results] - Delivery point address results
+ */
+
+/**
+ * @import { Request } from '@hapi/hapi'
+ * @import { FormPayload } from '~/src/server/plugins/engine/types.js'
+ */
diff --git a/src/server/plugins/postcode-lookup/views/postcode-lookup-details.html b/src/server/plugins/postcode-lookup/views/postcode-lookup-details.html
new file mode 100644
index 000000000..6e3d98482
--- /dev/null
+++ b/src/server/plugins/postcode-lookup/views/postcode-lookup-details.html
@@ -0,0 +1,83 @@
+{% extends baseLayoutPath %}
+
+{% from "govuk/components/error-summary/macro.njk" import govukErrorSummary %}
+{% from "govuk/components/input/macro.njk" import govukInput %}
+{% from "govuk/components/select/macro.njk" import govukSelect %}
+{% from "govuk/components/button/macro.njk" import govukButton %}
+{% from "govuk/components/inset-text/macro.njk" import govukInsetText %}
+{% from "govuk/components/hint/macro.njk" import govukHint %}
+{% from "govuk/components/fieldset/macro.njk" import govukFieldset %}
+
+{% block content %}
+  <div class="govuk-grid-row">
+    <div class="govuk-grid-column-two-thirds">
+      {% if errors %}
+        {{ govukErrorSummary({
+          titleText: "There is a problem",
+          errorList: errors
+        }) }}
+      {% endif %}
+
+      {% include "partials/heading.html" %}
+
+      <form method="post">
+        <input type="hidden" name="crumb" value="{{ crumb }}">
+        <input type="hidden" name="step" value="{{ step }}">
+
+        {% switch step %}
+          {% case "details" %}
+            <!-- Postcode lookup details -->
+            {{ govukInput(fields.postcodeQuery) }}
+            {{ govukInput(fields.buildingNameQuery) }}
+          {% case "select" %}
+            <!-- Postcode lookup select -->
+            <!-- Postcode lookup details display -->
+            {%- set detailsHtml -%}
+              <strong>{{ details.postcodeQuery }}</strong>{% if details.buildingNameQuery %} and <strong>{{ details.buildingNameQuery }}</strong>{% endif %}
+            {%- endset -%}
+
+            {% if hasAddresses %}
+              <p class="govuk-body">
+                {{addressCount}} address{{ "es" if hasMultipleAddresses }} found for {{ detailsHtml | safe }}. <a href="{{ searchAgainLink.href }}" class="govuk-link govuk-link--no-visited-state">{{ searchAgainLink.text }}</a>
+              </p>
+            {% endif %}
+
+            {% if hasMultipleAddresses %}
+              <!-- Multiple address found - show drop down select -->
+              {{ govukSelect(fields.uprn) }}
+            {% elif singleAddress %}
+              <!-- Single address found - show single item -->
+              {{ govukInput(fields.uprn) }}
+              {{ govukInsetText({
+                text: singleAddress.formatted
+              }) }}
+            {% else %}
+              <!-- No addresses found - show try again -->
+              <p class="govuk-body">We could not find an address that matches {{ detailsHtml | safe }}.</p>
+            {% endif %}
+          {% case "manual" %}
+            <!-- Postcode lookup manual entry -->
+            {% if hint %}
+              {{ govukHint(hint) }}
+            {% endif %}
+
+            {{ govukInput(fields.addressLine1) }}
+            {{ govukInput(fields.addressLine2) }}
+            {{ govukInput(fields.town) }}
+            {{ govukInput(fields.county) }}
+            {{ govukInput(fields.postcode) }}
+        {% endswitch %}
+
+        <div class="govuk-button-group">
+          {{ govukButton(buttons.continueButton) }}
+
+          {% if buttons.manualLink %}
+            <p class="govuk-body">or <a class="govuk-link govuk-link--no-visited-state" href="{{ buttons.manualLink.href }}">{{buttons.manualLink.text}}</a></p>
+          {% elif buttons.detailsLink %}
+            <p class="govuk-body">or <a class="govuk-link govuk-link--no-visited-state" href="{{ buttons.detailsLink.href }}">{{buttons.detailsLink.text}}</a></p>
+          {% endif %}
+        </div>
+      </form>
+    </div>
+  </div>
+{% endblock %}
diff --git a/src/server/postcode-lookup.test.ts b/src/server/postcode-lookup.test.ts
new file mode 100644
index 000000000..e8d468fcd
--- /dev/null
+++ b/src/server/postcode-lookup.test.ts
@@ -0,0 +1,64 @@
+import { type Server } from '@hapi/hapi'
+
+import { createServer } from '~/src/server/index.js'
+import { getFormMetadata } from '~/src/server/plugins/engine/services/formsService.js'
+import * as defaultServices from '~/src/server/plugins/engine/services/index.js'
+import * as fixtures from '~/test/fixtures/index.js'
+
+jest.mock('~/src/server/plugins/engine/services/formsService.js')
+jest.mock('~/src/server/plugins/engine/services/uploadService.js')
+
+describe('Postcode lookup plugin', () => {
+  let server: Server
+
+  beforeEach(() => {
+    jest.mocked(getFormMetadata).mockResolvedValue(fixtures.form.metadata)
+  })
+
+  afterAll(async () => {
+    await server.stop()
+  })
+
+  describe('Plugin registration', () => {
+    test('Registers plugin with ordnance survey key', async () => {
+      server = await createServer({
+        services: defaultServices,
+        ordnanceSurveyApiKey: 'dummy'
+      })
+      await server.initialize()
+
+      expect(server.registrations).toHaveProperty(
+        '@defra/forms-engine-plugin/postcode-lookup',
+        {
+          name: '@defra/forms-engine-plugin/postcode-lookup',
+          options: { ordnanceSurveyApiKey: 'dummy' },
+          version: undefined
+        }
+      )
+
+      expect(
+        server.table().find((route) => route.path === '/postcode-lookup')
+      ).toBeDefined()
+    })
+
+    test('Does not register plugin when no ordnance survey key is provided', async () => {
+      server = await createServer({
+        services: defaultServices
+      })
+      await server.initialize()
+
+      expect(server.registrations).not.toHaveProperty(
+        '@defra/forms-engine-plugin/postcode-lookup',
+        {
+          name: '@defra/forms-engine-plugin/postcode-lookup',
+          options: { ordnanceSurveyApiKey: 'dummy' },
+          version: undefined
+        }
+      )
+
+      expect(
+        server.table().find((route) => route.path === '/postcode-lookup')
+      ).toBeUndefined()
+    })
+  })
+})
diff --git a/src/server/routes/types.ts b/src/server/routes/types.ts
index 704fccac6..81ad60a12 100644
--- a/src/server/routes/types.ts
+++ b/src/server/routes/types.ts
@@ -48,10 +48,16 @@ export enum FormAction {
   Delete = 'delete',
   AddAnother = 'add-another',
   Send = 'send',
-  SaveAndExit = 'save-and-exit'
+  SaveAndExit = 'save-and-exit',
+  External = 'external'
 }
 
 export enum FormStatus {
   Draft = 'draft',
   Live = 'live'
 }
+
+export enum ExternalActions {
+  PostcodeLookup = 'postcode-lookup',
+  AnotherExternalAction = 'another-external-action'
+}
diff --git a/src/server/schemas/index.ts b/src/server/schemas/index.ts
index f181e7f01..b4e22af31 100644
--- a/src/server/schemas/index.ts
+++ b/src/server/schemas/index.ts
@@ -8,13 +8,11 @@ export const stateSchema = Joi.string<FormStatus>()
   .required()
 
 export const actionSchema = Joi.string<FormAction>()
-  .valid(
-    FormAction.Continue,
-    FormAction.Validate,
-    FormAction.Delete,
-    FormAction.AddAnother,
-    FormAction.Send,
-    FormAction.SaveAndExit
+  .pattern(new RegExp(`^${FormAction.External}-[a-zA-Z-:]*$`))
+  .allow(
+    ...Object.values(FormAction).filter(
+      (value) => value !== FormAction.External
+    )
   )
   .default(FormAction.Validate)
   .optional()
diff --git a/src/server/types.ts b/src/server/types.ts
index b5179ae00..b20881f28 100644
--- a/src/server/types.ts
+++ b/src/server/types.ts
@@ -53,6 +53,7 @@ export interface RouteConfig {
   onRequest?: OnRequestCallback
   saveAndExit?: PluginOptions['saveAndExit']
   cacheServiceCreator?: (server: Server) => CacheService
+  ordnanceSurveyApiKey?: string
 }
 
 export interface OutputService {
diff --git a/test/form/definitions/postcode-lookup.js b/test/form/definitions/postcode-lookup.js
new file mode 100644
index 000000000..68cd472d9
--- /dev/null
+++ b/test/form/definitions/postcode-lookup.js
@@ -0,0 +1,49 @@
+import {
+  ComponentType,
+  ControllerType,
+  Engine,
+  SchemaVersion
+} from '@defra/forms-model'
+
+export default /** @satisfies {FormDefinition} */ ({
+  name: 'UkAddressField with Postcode lookup',
+  engine: Engine.V2,
+  schema: SchemaVersion.V2,
+  startPage: '/address',
+  pages: [
+    {
+      title: 'Address',
+      path: '/address',
+      components: [
+        {
+          type: ComponentType.UkAddressField,
+          title: 'What is your address?',
+          name: 'ybMHIv',
+          shortDescription: 'Address',
+          hint: '',
+          options: {
+            required: true,
+            usePostcodeLookup: true
+          },
+          id: 'ebc6cc6d-2596-4860-b62d-98510b277ac4'
+        }
+      ],
+      next: [],
+      id: 'c7ab16e8-819a-43bd-83fa-14c479d23961'
+    },
+    {
+      title: 'Summary',
+      path: '/summary',
+      controller: ControllerType.Summary,
+      components: [],
+      id: '8d2aba52-314e-4a5b-b502-47e205877de5'
+    }
+  ],
+  conditions: [],
+  sections: [],
+  lists: []
+})
+
+/**
+ * @import { FormDefinition } from '@defra/forms-model'
+ */
diff --git a/test/form/fields-optional.test.js b/test/form/fields-optional.test.js
index 8df8bd1ef..61c8c1833 100644
--- a/test/form/fields-optional.test.js
+++ b/test/form/fields-optional.test.js
@@ -95,7 +95,8 @@ describe('Form fields (optional)', () => {
               addressField__addressLine2: '',
               addressField__town: '',
               addressField__county: '',
-              addressField__postcode: ''
+              addressField__postcode: '',
+              addressField__uprn: ''
             }
           }
         },
diff --git a/test/form/fields-required.test.js b/test/form/fields-required.test.js
index acf08d397..b2b146446 100644
--- a/test/form/fields-required.test.js
+++ b/test/form/fields-required.test.js
@@ -111,14 +111,16 @@ describe('Form fields (required)', () => {
               addressField__addressLine2: '',
               addressField__town: '',
               addressField__county: '',
-              addressField__postcode: ''
+              addressField__postcode: '',
+              addressField__uprn: ''
             },
             valid: {
               addressField__addressLine1: 'Richard Fairclough House',
               addressField__addressLine2: 'Knutsford Road',
               addressField__town: 'Warrington',
               addressField__county: 'Cheshire',
-              addressField__postcode: 'WA4 1HT'
+              addressField__postcode: 'WA4 1HT',
+              addressField__uprn: ''
             }
           }
         },
diff --git a/test/form/govuk-notify.test.js b/test/form/govuk-notify.test.js
index 4faa98f55..7a4b1b3b7 100644
--- a/test/form/govuk-notify.test.js
+++ b/test/form/govuk-notify.test.js
@@ -358,6 +358,7 @@ describe('Submission journey test', () => {
       addressField__town: 'Town or city',
       addressField__county: 'Cheshire',
       addressField__postcode: 'CW1 1AB',
+      addressField__uprn: '',
       radiosField: 'privateLimitedCompany',
       selectField: '910400000',
       autocompleteField: '910400044',
diff --git a/test/form/postcode-lookup.test.js b/test/form/postcode-lookup.test.js
new file mode 100644
index 000000000..cb1570564
--- /dev/null
+++ b/test/form/postcode-lookup.test.js
@@ -0,0 +1,605 @@
+import { join } from 'node:path'
+
+import { within } from '@testing-library/dom'
+import { StatusCodes } from 'http-status-codes'
+
+import { FORM_PREFIX } from '~/src/server/constants.js'
+import { createServer } from '~/src/server/index.js'
+import { getFormMetadata } from '~/src/server/plugins/engine/services/formsService.js'
+import {
+  search,
+  searchByUPRN
+} from '~/src/server/plugins/postcode-lookup/service.js'
+import * as fixtures from '~/test/fixtures/index.js'
+import { renderResponse } from '~/test/helpers/component-helpers.js'
+import { getCookie, getCookieHeader } from '~/test/utils/get-cookie.js'
+const basePath = `${FORM_PREFIX}/postcode-lookup`
+
+jest.mock('~/src/server/plugins/engine/services/formsService.js')
+jest.mock('~/src/server/plugins/postcode-lookup/service.js')
+
+/**
+ *
+ * @param {Server} server
+ */
+async function initialiseJourney(server) {
+  const response = await server.inject({
+    url: `${basePath}/address`
+  })
+
+  // Extract the session cookie
+  const csrfToken = getCookie(response, 'crumb')
+  const headers = getCookieHeader(response, ['session', 'crumb'])
+
+  return { csrfToken, response, headers }
+}
+
+describe('Postcode lookup form pages', () => {
+  /** @type {Server} */
+  let server
+
+  beforeAll(async () => {
+    server = await createServer({
+      formFileName: 'postcode-lookup.js',
+      formFilePath: join(import.meta.dirname, 'definitions'),
+      enforceCsrf: true,
+      ordnanceSurveyApiKey: 'dummy'
+    })
+
+    await server.initialize()
+  })
+
+  beforeEach(() => {
+    jest.mocked(getFormMetadata).mockResolvedValue(fixtures.form.metadata)
+  })
+
+  it('should render the source form page with a postcode lookup buttons', async () => {
+    const { container } = await renderResponse(server, {
+      url: `${basePath}/address`
+    })
+
+    const $actionButton = container.getByRole('button', {
+      name: 'Find an address'
+    })
+
+    expect($actionButton).toBeInTheDocument()
+    expect($actionButton.getAttribute('name')).toBe('action')
+    expect($actionButton.getAttribute('value')).toBe('external-ybMHIv')
+
+    const $manualButton = container.getByRole('button', {
+      name: 'enter address manually'
+    })
+
+    expect($manualButton).toBeInTheDocument()
+    expect($manualButton.getAttribute('name')).toBe('action')
+    expect($manualButton.getAttribute('value')).toBe(
+      'external-ybMHIv--step:manual'
+    )
+  })
+
+  it('should return a single validation message', async () => {
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    const payload = {
+      crumb: csrfToken
+    }
+
+    const { response, container } = await renderResponse(server, {
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+
+    const $errorSummary = container.getByRole('alert')
+    const $heading = within($errorSummary).getByRole('heading', {
+      name: 'There is a problem',
+      level: 2
+    })
+    expect($heading).toBeInTheDocument()
+
+    const $errorItems = within($errorSummary).getAllByRole('listitem')
+    expect($errorItems).toHaveLength(1)
+    expect($errorItems[0]).toHaveTextContent('Enter address')
+  })
+
+  it('should dispatch to details page on POST', async () => {
+    let { csrfToken, response, headers } = await initialiseJourney(server)
+
+    const payload = {
+      action: 'external-ybMHIv',
+      crumb: csrfToken
+    }
+
+    response = await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.SEE_OTHER)
+    expect(response.headers.location).toBe('/postcode-lookup')
+  })
+
+  it('should dispatch to manual page on POST with step arg', async () => {
+    let { csrfToken, response, headers } = await initialiseJourney(server)
+
+    const payload = {
+      action: 'external-ybMHIv--step:manual',
+      crumb: csrfToken
+    }
+
+    response = await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.SEE_OTHER)
+    expect(response.headers.location).toBe('/postcode-lookup?step=manual')
+  })
+
+  it('should render the details page', async () => {
+    let { csrfToken, response, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    const payload = {
+      action: 'external-ybMHIv',
+      crumb: csrfToken
+    }
+
+    response = await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.SEE_OTHER)
+    expect(response.headers.location).toBe('/postcode-lookup')
+
+    headers = getCookieHeader(response, ['session'])
+
+    response = await server.inject({
+      url: '/postcode-lookup',
+      method: 'GET',
+      headers
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+  })
+
+  it('should render the manual page', async () => {
+    let { csrfToken, response, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    const payload = {
+      action: 'external-ybMHIv--step:manual',
+      crumb: csrfToken
+    }
+
+    response = await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.SEE_OTHER)
+    expect(response.headers.location).toBe('/postcode-lookup?step=manual')
+
+    headers = getCookieHeader(response, ['session'])
+
+    response = await server.inject({
+      url: '/postcode-lookup?step=manual',
+      method: 'GET',
+      headers
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+  })
+
+  it('should render validation errors after POST when no postcode is provided', async () => {
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    const { response, container } = await renderResponse(server, {
+      url: '/postcode-lookup',
+      method: 'POST',
+      headers,
+      payload: {
+        step: 'details',
+        postcodeQuery: '',
+        buildingNameQuery: '',
+        crumb: csrfToken
+      }
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+    const $errorSummary = container.getByRole('alert')
+
+    const $heading = within($errorSummary).getByRole('heading', {
+      name: 'There is a problem',
+      level: 2
+    })
+    expect($heading).toBeInTheDocument()
+  })
+
+  it('should render the select page after POST when multiple addresses are found', async () => {
+    jest.mocked(search).mockResolvedValueOnce([
+      {
+        address:
+          'PRIME MINISTER & FIRST LORD OF THE TREASURY, 10, DOWNING STREET, LONDON, SW1A 2AA',
+        addressLine1: 'Prime Minister & First Lord Of The Treasury 10',
+        addressLine2: 'Downing Street',
+        county: '',
+        formatted:
+          'Prime Minister & First Lord Of The Treasury 10, Downing Street, London, SW1A 2AA',
+        postcode: 'SW1A 2AA',
+        town: 'London',
+        uprn: '100023336956'
+      },
+      {
+        address:
+          'CHANCELLOR & FIRST LORD OF THE TREASURY, 10, DOWNING STREET, LONDON, SW1A 2AA',
+        addressLine1: 'Chancellor & First Lord Of The Treasury 11',
+        addressLine2: 'Downing Street',
+        county: '',
+        formatted:
+          'Chancellor & First Lord Of The Treasury 10, Downing Street, London, SW1A 2AA',
+        postcode: 'SW1A 2AA',
+        town: 'London',
+        uprn: '100023336957'
+      }
+    ])
+
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    const { response: selectResponse, container } = await renderResponse(
+      server,
+      {
+        url: '/postcode-lookup',
+        method: 'POST',
+        headers,
+        payload: {
+          step: 'details',
+          postcodeQuery: 'SW1A 2AA',
+          buildingNameQuery: '',
+          crumb: csrfToken
+        }
+      }
+    )
+
+    expect(selectResponse.statusCode).toBe(StatusCodes.OK)
+
+    const $addressSelector = container.getByRole('combobox')
+    expect($addressSelector).toBeInTheDocument()
+
+    const $addressSelectorOptions = container.getAllByRole('option')
+    expect($addressSelectorOptions).toHaveLength(3)
+
+    const $useAddressButton = container.getByRole('button', {
+      name: 'Use this address'
+    })
+
+    expect($useAddressButton).toBeInTheDocument()
+  })
+
+  it('should render the select page after POST when a single address is found', async () => {
+    jest.mocked(search).mockResolvedValueOnce([
+      {
+        address: 'SHERLOCK HOLMES MUSEUM, 221B, BAKER STREET, LONDON, NW1 6XE',
+        addressLine1: 'Sherlock Holmes Museum 221b',
+        addressLine2: 'Baker Street',
+        county: '',
+        formatted: 'Sherlock Holmes Museum 221b, Baker Street, London, NW1 6XE',
+        postcode: 'NW1 6XE',
+        town: 'London',
+        uprn: '100023071949'
+      }
+    ])
+
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    const { response: selectResponse, container } = await renderResponse(
+      server,
+      {
+        url: '/postcode-lookup',
+        method: 'POST',
+        headers,
+        payload: {
+          step: 'details',
+          postcodeQuery: 'NW1 6XE',
+          buildingNameQuery: '221B',
+          crumb: csrfToken
+        }
+      }
+    )
+
+    expect(selectResponse.statusCode).toBe(StatusCodes.OK)
+
+    const $addressPostcodeDisplay = container.getByText('NW1 6XE', {
+      selector: 'strong'
+    })
+    expect($addressPostcodeDisplay).toBeInTheDocument()
+
+    const $addressBuildingNameDisplay = container.getByText('221B', {
+      selector: 'strong'
+    })
+    expect($addressBuildingNameDisplay).toBeInTheDocument()
+
+    const $addressDisplay = container.getByText(
+      'Sherlock Holmes Museum 221b, Baker Street, London, NW1 6XE'
+    )
+    expect($addressDisplay).toBeInTheDocument()
+
+    const $useAddressButton = container.getByRole('button', {
+      name: 'Use this address'
+    })
+
+    expect($useAddressButton).toBeInTheDocument()
+  })
+
+  it('should render the select page after POST when a no addresses are found', async () => {
+    jest.mocked(search).mockResolvedValueOnce([])
+
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    const { response: selectResponse, container } = await renderResponse(
+      server,
+      {
+        url: '/postcode-lookup',
+        method: 'POST',
+        headers,
+        payload: {
+          step: 'details',
+          postcodeQuery: 'AA1 1AA',
+          buildingNameQuery: '100',
+          crumb: csrfToken
+        }
+      }
+    )
+
+    expect(selectResponse.statusCode).toBe(StatusCodes.OK)
+
+    const $noAddressesFound = container.getByRole('heading', {
+      name: 'No address found',
+      level: 1
+    })
+    expect($noAddressesFound).toBeInTheDocument()
+  })
+
+  it('should redirect back to the source page after POST when multiple addresses are found', async () => {
+    jest.mocked(searchByUPRN).mockResolvedValueOnce([
+      {
+        address:
+          'PRIME MINISTER & FIRST LORD OF THE TREASURY, 10, DOWNING STREET, LONDON, SW1A 2AA',
+        addressLine1: 'Prime Minister & First Lord Of The Treasury 10',
+        addressLine2: 'Downing Street',
+        county: '',
+        formatted:
+          'Prime Minister & First Lord Of The Treasury 10, Downing Street, London, SW1A 2AA',
+        postcode: 'SW1A 2AA',
+        town: 'London',
+        uprn: '100023336956'
+      }
+    ])
+
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    let { response } = await renderResponse(server, {
+      url: '/postcode-lookup',
+      method: 'POST',
+      headers,
+      payload: {
+        step: 'select',
+        uprn: '100023336956',
+        crumb: csrfToken
+      }
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.SEE_OTHER)
+    expect(response.headers.location).toEndWith('/address')
+
+    // Follow the redirect back to the source
+    // page to exercise `importExternalComponentState`
+    response = await server.inject({
+      url: `${basePath}/address`,
+      headers
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+  })
+
+  it('should render validation errors after POST when no address is selected', async () => {
+    jest.mocked(search).mockResolvedValueOnce([
+      {
+        address:
+          'PRIME MINISTER & FIRST LORD OF THE TREASURY, 10, DOWNING STREET, LONDON, SW1A 2AA',
+        addressLine1: 'Prime Minister & First Lord Of The Treasury 10',
+        addressLine2: 'Downing Street',
+        county: '',
+        formatted:
+          'Prime Minister & First Lord Of The Treasury 10, Downing Street, London, SW1A 2AA',
+        postcode: 'SW1A 2AA',
+        town: 'London',
+        uprn: '100023336956'
+      }
+    ])
+
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    const { response, container } = await renderResponse(server, {
+      url: '/postcode-lookup',
+      method: 'POST',
+      headers,
+      payload: {
+        step: 'select',
+        crumb: csrfToken
+      }
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+    const $errorSummary = container.getByRole('alert')
+
+    const $heading = within($errorSummary).getByRole('heading', {
+      name: 'There is a problem',
+      level: 2
+    })
+    expect($heading).toBeInTheDocument()
+  })
+
+  it('should render validation errors after POST to manual page when no address lines are provided', async () => {
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    const { response, container } = await renderResponse(server, {
+      url: '/postcode-lookup?step=manual',
+      method: 'POST',
+      headers,
+      payload: {
+        step: 'manual',
+        addressLine1: '',
+        addressLine2: '',
+        town: '',
+        county: '',
+        postcode: '',
+        crumb: csrfToken
+      }
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+    const $errorSummary = container.getByRole('alert')
+
+    const $heading = within($errorSummary).getByRole('heading', {
+      name: 'There is a problem',
+      level: 2
+    })
+    expect($heading).toBeInTheDocument()
+  })
+
+  it('should redirect back to the source page after successful POST to manual page', async () => {
+    const { csrfToken, headers } = await initialiseJourney(server)
+
+    // Dispatch to postcode journey
+    await server.inject({
+      url: `${basePath}/address`,
+      method: 'POST',
+      headers,
+      payload: {
+        action: 'external-ybMHIv',
+        crumb: csrfToken
+      }
+    })
+
+    let { response } = await renderResponse(server, {
+      url: '/postcode-lookup?step=manual',
+      method: 'POST',
+      headers,
+      payload: {
+        step: 'manual',
+        addressLine1: '1 Street Name',
+        addressLine2: '',
+        town: 'Middletown',
+        county: '',
+        postcode: 'M15 5TN',
+        crumb: csrfToken
+      }
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.SEE_OTHER)
+    expect(response.headers.location).toEndWith('/address')
+
+    // Follow the redirect back to the source
+    // page to exercise `importExternalComponentState`
+    response = await server.inject({
+      url: `${basePath}/address`,
+      headers
+    })
+
+    expect(response.statusCode).toBe(StatusCodes.OK)
+  })
+})
+
+/**
+ * @import { Server } from '@hapi/hapi'
+ */