diff --git a/src/__mocks__/logger-mocks.js b/src/__mocks__/logger-mocks.js
index 259c090da..07f28d78a 100644
--- a/src/__mocks__/logger-mocks.js
+++ b/src/__mocks__/logger-mocks.js
@@ -1,5 +1,5 @@
 import { vi } from 'vitest'
-import { LogCodes } from '~/src/server/common/helpers/logging/log-codes-definition.js'
+import { LogCodes } from '~/src/server/common/helpers/logging/log-codes/definition.js'
 
 export const mockLoggerFactory = () => ({
   info: vi.fn(),
@@ -15,14 +15,14 @@ export const mockLoggerFactoryWithCustomMethods = (customMethods = {}) => ({
 
 /**
  * @typedef {Object} MockLogCodesDefinition
- * @property {import('~/src/server/common/helpers/logging/log-codes-definition.js').LogTypes.LogLevel} level
+ * @property {import('~/src/server/common/helpers/logging/log-codes/definition.js').LogTypes.LogLevel} level
  * @property {import('vitest').Mock} messageFunc
  */
 
 /**
  * Auto-generate mock LogCodes from real LogCodes
  * Each messageFunc becomes a vi.fn() for test assertions
- * @param {typeof import('~/src/server/common/helpers/logging/log-codes-definition.js').LogCodes} codes
+ * @param {typeof import('~/src/server/common/helpers/logging/log-codes/definition.js').LogCodes} codes
  * @returns {Record<string, Record<string, MockLogCodesDefinition>>}
  */
 const autoMockLogCodes = (codes) =>
diff --git a/src/contracts/grants-ui-gas.contract.test.js b/src/contracts/grants-ui-gas.contract.test.js
index 363b84116..8ff42aa6d 100644
--- a/src/contracts/grants-ui-gas.contract.test.js
+++ b/src/contracts/grants-ui-gas.contract.test.js
@@ -8,11 +8,10 @@ vi.mock('../server/common/helpers/retry.js', () => ({
   retry: (operation) => operation()
 }))
 
-vi.mock('../server/common/helpers/logging/log.js', () => ({
-  debug: vi.fn(),
-  log: vi.fn(),
-  logger: { debug: vi.fn(), info: vi.fn(), error: vi.fn(), warn: vi.fn() }
-}))
+vi.mock('../server/common/helpers/logging/log.js', async () => {
+  const { mockLogHelper } = await import('../__mocks__/logger-mocks.js')
+  return mockLogHelper()
+})
 
 function createProvider() {
   return new PactV4({
diff --git a/src/contracts/v1/land-grants.client.contract.test.js b/src/contracts/v1/land-grants.client.contract.test.js
index 64d9747e5..896bd7138 100644
--- a/src/contracts/v1/land-grants.client.contract.test.js
+++ b/src/contracts/v1/land-grants.client.contract.test.js
@@ -3,18 +3,10 @@ import path from 'path'
 import { vi } from 'vitest'
 import { postToLandGrantsApi } from '~/src/server/land-grants/services/land-grants.client'
 
-vi.mock('~/src/server/common/helpers/logging/log.js', () => ({
-  LogCodes: {
-    LAND_GRANTS: {
-      API_REQUEST: { level: 'info', messageFunc: vi.fn() }
-    }
-  },
-  log: vi.fn(),
-  debug: vi.fn(),
-  logger: {
-    debug: vi.fn()
-  }
-}))
+vi.mock('~/src/server/common/helpers/logging/log.js', async () => {
+  const { mockLogHelper } = await import('~/src/__mocks__/logger-mocks.js')
+  return mockLogHelper()
+})
 
 vi.mock('~/src/server/common/helpers/retry.js', () => ({
   retry: (operation) => operation()
diff --git a/src/contracts/v2/land-grants.client.contract.test.js b/src/contracts/v2/land-grants.client.contract.test.js
index 17507cf4d..912274b96 100644
--- a/src/contracts/v2/land-grants.client.contract.test.js
+++ b/src/contracts/v2/land-grants.client.contract.test.js
@@ -4,18 +4,10 @@ import path from 'path'
 import { vi } from 'vitest'
 import { postToLandGrantsApi } from '~/src/server/land-grants/services/land-grants.client'
 
-vi.mock('~/src/server/common/helpers/logging/log.js', () => ({
-  LogCodes: {
-    LAND_GRANTS: {
-      API_REQUEST: { level: 'info', messageFunc: vi.fn() }
-    }
-  },
-  log: vi.fn(),
-  debug: vi.fn(),
-  logger: {
-    debug: vi.fn()
-  }
-}))
+vi.mock('~/src/server/common/helpers/logging/log.js', async () => {
+  const { mockLogHelper } = await import('~/src/__mocks__/logger-mocks.js')
+  return mockLogHelper()
+})
 
 vi.mock('~/src/server/common/helpers/retry.js', () => ({
   retry: (operation) => operation()
diff --git a/src/server/agreements/controller.js b/src/server/agreements/controller.js
index 28ed115cb..0aaa90957 100644
--- a/src/server/agreements/controller.js
+++ b/src/server/agreements/controller.js
@@ -2,7 +2,7 @@ import { config } from '~/src/config/config.js'
 import { statusCodes } from '~/src/server/common/constants/status-codes.js'
 import Jwt from '@hapi/jwt'
 import { SystemError } from '~/src/server/common/utils/errors/SystemError.js'
-import { log, debug } from '~/src/server/common/helpers/logging/log.js'
+import { log } from '~/src/server/common/helpers/logging/log.js'
 import { LogCodes } from '~/src/server/common/helpers/logging/log-codes.js'
 
 /**
@@ -76,6 +76,19 @@ function buildProxyHeaders(token, request) {
   }
 }
 
+function logAgreementsUpstreamError(request, error) {
+  log(
+    LogCodes.SYSTEM.EXTERNAL_API_ERROR,
+    {
+      endpoint: 'agreements',
+      service: 'farming-grants-agreements-ui',
+      upstreamStatus: error.statusCode ?? error.output?.statusCode ?? error.status ?? null,
+      errorMessage: error.message
+    },
+    request
+  )
+}
+
 /**
  * Controller for the agreements API
  * @satisfies {Partial<ServerRoute>}
@@ -108,7 +121,7 @@ export const getAgreementController = {
 
       return apiResponse
     } catch (error) {
-      debug(LogCodes.SYSTEM.EXTERNAL_API_ERROR, { endpoint: 'agreements', errorMessage: error.message }, request)
+      logAgreementsUpstreamError(request, error)
 
       if (error.message.includes('Missing required configuration')) {
         return h
diff --git a/src/server/agreements/controller.test.js b/src/server/agreements/controller.test.js
index ff148430c..7b29d4997 100644
--- a/src/server/agreements/controller.test.js
+++ b/src/server/agreements/controller.test.js
@@ -3,6 +3,7 @@ import { getAgreementController } from './controller.js'
 import { config } from '~/src/config/config.js'
 import Jwt from '@hapi/jwt'
 import { mockHapiRequest, mockHapiResponseToolkit } from '~/src/__mocks__/hapi-mocks.js'
+import { log } from '~/src/server/common/helpers/logging/log.js'
 
 vi.mock('~/src/config/config.js', async () => {
   const { mockConfigSimple } = await import('~/src/__mocks__')
@@ -449,6 +450,25 @@ describe('Agreements Controller', () => {
       })
     })
 
+    test('should log EXTERNAL_API_ERROR with service and upstreamStatus on proxy 5xx', async () => {
+      const proxyError = new Error('Bad Gateway')
+      proxyError.output = { statusCode: 502 }
+      mockH.proxy.mockRejectedValue(proxyError)
+
+      await getAgreementController.handler(mockRequest, mockH)
+
+      expect(log).toHaveBeenCalledWith(
+        expect.objectContaining({ level: 'error' }),
+        expect.objectContaining({
+          endpoint: 'agreements',
+          service: 'farming-grants-agreements-ui',
+          upstreamStatus: 502,
+          errorMessage: 'Bad Gateway'
+        }),
+        mockRequest
+      )
+    })
+
     test('should not include error details in production', async () => {
       const originalNodeEnv = process.env.NODE_ENV
       process.env.NODE_ENV = 'production'
diff --git a/src/server/auth/services/whitelist.service.js b/src/server/auth/services/whitelist.service.js
index 9884c95e9..5dbe4b5c8 100644
--- a/src/server/auth/services/whitelist.service.js
+++ b/src/server/auth/services/whitelist.service.js
@@ -122,7 +122,7 @@ class WhitelistService {
   /**
    * Helper method to log whitelist events with consistent structure
    * @param {object} logCode - Logging options.
-   * @param {import('../../common/helpers/logging/log-codes-definition.js').LogTypes.LogLevel} logCode.level - The log level.
+   * @param {import('../../common/helpers/logging/log-codes/definition.js').LogTypes.LogLevel} logCode.level - The log level.
    * @param {Function} logCode.messageFunc - A function that creates an interpolated message string
    * @param {string} crn - The user's CRN
    * @param {string} sbi - The SBI number
diff --git a/src/server/common/helpers/errors.js b/src/server/common/helpers/errors.js
index d7e33fafd..db2dd56e8 100644
--- a/src/server/common/helpers/errors.js
+++ b/src/server/common/helpers/errors.js
@@ -15,6 +15,7 @@ import { config } from '~/src/config/config.js'
 import { BaseError } from '~/src/server/common/utils/errors/BaseError.js'
 
 const UNKNOWN_USER = 'unknown'
+const SERVER_ERROR_RANGE_END = 600
 
 export const HTTP_STATUS = {
   BAD_REQUEST: 400,
@@ -74,6 +75,24 @@ function statusCodeMessage(statusCode) {
   }
 }
 
+/**
+ * Reads the upstream HTTP status from a thrown error wrapped by Boom, so it can
+ * be attached to the SERVER_ERROR log payload. When a downstream service
+ * (e.g. grants-ui-backend) responds with 5xx, the call site throws an Error
+ * with `code`/`status` set; `boomify` mutates that error in place to add Boom
+ * fields without removing the original properties.
+ * @param {ErrorResponse} response
+ * @returns {number | null}
+ */
+function getUpstreamStatus(response) {
+  const candidate = response?.code ?? response?.status ?? null
+  return typeof candidate === 'number' &&
+    candidate >= statusCodes.internalServerError &&
+    candidate < SERVER_ERROR_RANGE_END
+    ? candidate
+    : null
+}
+
 /**
  * @param { AnyRequest } request
  * @param { ResponseToolkit } h
@@ -86,6 +105,7 @@ export function catchAll(request, h) {
   }
 
   let statusCode
+  let upstreamStatus = null
 
   if (response instanceof BaseError) {
     const rootErrors = BaseError.findRootErrors(response)
@@ -95,7 +115,8 @@ export function catchAll(request, h) {
     statusCode = response.details.status || statusCodes.internalServerError
   } else {
     statusCode = response.output.statusCode || statusCodes.internalServerError
-    handleErrorLogging(request, response, statusCode)
+    upstreamStatus = getUpstreamStatus(response)
+    handleErrorLogging(request, response, statusCode, upstreamStatus)
   }
 
   // Handle redirects properly
@@ -106,9 +127,15 @@ export function catchAll(request, h) {
   return renderErrorView(h, statusCode)
 }
 
-function handleErrorLogging(request, response, statusCode) {
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {number} statusCode
+ * @param {number | null} [upstreamStatus]
+ */
+function handleErrorLogging(request, response, statusCode, upstreamStatus = null) {
   if (statusCode >= statusCodes.internalServerError) {
-    handleServerErrors(request, response, statusCode)
+    handleServerErrors(request, response, statusCode, upstreamStatus)
   } else if (statusCode >= statusCodes.badRequest) {
     handleClientErrors(request, response, statusCode)
   } else {
@@ -116,7 +143,13 @@ function handleErrorLogging(request, response, statusCode) {
   }
 }
 
-function handleServerErrors(request, response, statusCode) {
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {number} statusCode
+ * @param {number | null} [upstreamStatus]
+ */
+function handleServerErrors(request, response, statusCode, upstreamStatus = null) {
   const errorContext = analyzeError(request, response)
 
   if (errorContext.isAuthError && !errorContext.alreadyLogged) {
@@ -124,7 +157,7 @@ function handleServerErrors(request, response, statusCode) {
   } else if (errorContext.isBellError && !errorContext.alreadyLogged) {
     logBellError(request, response, errorContext)
   } else if (!errorContext.isAuthError && !errorContext.isBellError && !errorContext.alreadyLogged) {
-    logSystemError(request, response, statusCode)
+    logSystemError(request, response, statusCode, upstreamStatus)
   } else {
     // Error already logged, skip to avoid duplicates
   }
@@ -132,6 +165,11 @@ function handleServerErrors(request, response, statusCode) {
   logDebugInformation(request, response, statusCode, errorContext)
 }
 
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @returns {ErrorContext}
+ */
 function analyzeError(request, response) {
   return {
     isAuthError: request.path?.startsWith('/auth'),
@@ -140,6 +178,10 @@ function analyzeError(request, response) {
   }
 }
 
+/**
+ * @param {ErrorResponse} response
+ * @returns {boolean | undefined}
+ */
 function isBellRelatedError(response) {
   return (
     response?.message?.includes('bell') ||
@@ -149,6 +191,11 @@ function isBellRelatedError(response) {
   )
 }
 
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {ErrorContext} errorContext
+ */
 function logAuthError(request, response, errorContext) {
   log(
     LogCodes.AUTH.SIGN_IN_FAILURE,
@@ -162,6 +209,11 @@ function logAuthError(request, response, errorContext) {
   )
 }
 
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {ErrorContext} errorContext
+ */
 function logBellError(request, response, errorContext) {
   log(
     LogCodes.AUTH.SIGN_IN_FAILURE,
@@ -175,6 +227,12 @@ function logBellError(request, response, errorContext) {
   )
 }
 
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {ErrorContext} errorContext
+ * @returns {Record<string, unknown>}
+ */
 function buildAuthContext(request, response, errorContext) {
   return {
     path: request.path,
@@ -194,12 +252,19 @@ function buildAuthContext(request, response, errorContext) {
   }
 }
 
-function logSystemError(request, response, statusCode) {
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {number} statusCode
+ * @param {number | null} [upstreamStatus]
+ */
+function logSystemError(request, response, statusCode, upstreamStatus = null) {
   log(
     LogCodes.SYSTEM.SERVER_ERROR,
     {
       errorMessage: response?.message || 'Internal server error',
       statusCode,
+      ...(upstreamStatus ? { upstreamStatus } : {}),
       path: request.path,
       method: request.method,
       stack: response?.stack
@@ -208,6 +273,12 @@ function logSystemError(request, response, statusCode) {
   )
 }
 
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {number} statusCode
+ * @param {ErrorContext} errorContext
+ */
 function logDebugInformation(request, response, statusCode, errorContext) {
   const errorMessage = statusCodeMessage(statusCode)
 
@@ -241,9 +312,14 @@ function logDebugInformation(request, response, statusCode, errorContext) {
   )
 }
 
+/**
+ * @param {AnyRequest} request
+ * @param {ErrorResponse} response
+ * @param {number} statusCode
+ */
 function handleClientErrors(request, response, statusCode) {
   if (statusCode === statusCodes.locked) {
-    // Expected business condition – no system error log
+    // Expected business condition - no system error log
     return
   }
   const errorMessage = statusCodeMessage(statusCode)
@@ -298,7 +374,7 @@ function tryParseForm(path, errorMsg) {
 /**
  * Parse resource path to determine type and context
  * @param {string} path - Request path
- * @param {object} response - Response object
+ * @param {ErrorResponse} response - Response object
  * @returns {{type: string, identifier: string, reason: string}}
  */
 function parseResourcePath(path, response) {
@@ -315,7 +391,7 @@ function parseResourcePath(path, response) {
 /**
  * Handle 404 errors with detailed context logging
  * @param {AnyRequest} request
- * @param {object} response
+ * @param {ErrorResponse} response
  */
 function handle404WithContext(request, response) {
   const path = request.path || 'unknown'
@@ -357,6 +433,10 @@ function handle404WithContext(request, response) {
   }
 }
 
+/**
+ * @param {ResponseToolkit} h
+ * @param {number} statusCode
+ */
 function renderErrorView(h, statusCode) {
   // SonarQube does not like this being set as the default for the switch, it's apparently a critical issue.
   let errorView
@@ -395,6 +475,17 @@ function renderErrorView(h, statusCode) {
 }
 
 /**
+ * @typedef {Object} ErrorContext
+ * @property {boolean} [isAuthError] - Whether the request is for an /auth path
+ * @property {boolean} [alreadyLogged] - Whether the error has already been logged upstream
+ * @property {boolean} [isBellError] - Whether the error originates from Bell/OAuth
+ *
+ * @typedef {Boom & { code?: number, status?: number, alreadyLogged?: boolean }} ErrorResponse
+ *   A Boom error, optionally augmented with `code`/`status` (set by upstream
+ *   client code before `boomify` wraps the Error) and `alreadyLogged` (set by
+ *   handlers that have already emitted a log entry to suppress duplicates).
+ *
+ * @import { Boom } from '@hapi/boom'
  * @import { AnyRequest } from '@defra/forms-engine-plugin/engine/types.js'
  * @import { ResponseToolkit } from '@hapi/hapi'
  */
diff --git a/src/server/common/helpers/errors.test.js b/src/server/common/helpers/errors.test.js
index 717afe35a..f862a697a 100644
--- a/src/server/common/helpers/errors.test.js
+++ b/src/server/common/helpers/errors.test.js
@@ -191,6 +191,26 @@ describe('#catchAll', () => {
     expect(mockToolkitCode).toHaveBeenCalledWith(statusCodes.imATeapot)
   })
 
+  test('Should include upstreamStatus in the SERVER_ERROR log payload when the response carries an upstream 5xx', () => {
+    const request = mockRequest(statusCodes.internalServerError)
+    request.response.code = statusCodes.badGateway
+    request.response.status = statusCodes.badGateway
+
+    catchAll(request, mockToolkit)
+
+    expect(log).toHaveBeenCalledWith(
+      expect.objectContaining({ level: 'error' }),
+      expect.objectContaining({
+        upstreamStatus: statusCodes.badGateway,
+        statusCode: statusCodes.internalServerError
+      }),
+      request
+    )
+    // Response status is unchanged — 500 stays 500 user-facing.
+    expect(mockToolkitView).toHaveBeenCalledWith('errors/500', { supportEmail: null })
+    expect(mockToolkitCode).toHaveBeenCalledWith(statusCodes.internalServerError)
+  })
+
   test('Should provide expected "Something went wrong" page and log error for internalServerError', () => {
     catchAll(mockRequest(statusCodes.internalServerError), mockToolkit)
 
diff --git a/src/server/common/helpers/lock/application-lock.js b/src/server/common/helpers/lock/application-lock.js
index 7a3a963a3..a14ec17a7 100644
--- a/src/server/common/helpers/lock/application-lock.js
+++ b/src/server/common/helpers/lock/application-lock.js
@@ -1,10 +1,27 @@
 import { createApiHeadersForGrantsUiBackend } from '../auth/backend-auth-helper.js'
-import { log, debug, LogCodes } from '~/src/server/common/helpers/logging/log.js'
+import { log, LogCodes } from '~/src/server/common/helpers/logging/log.js'
 import { mintLockReleaseToken } from './lock-token.js'
 import { config } from '~/src/config/config.js'
 
 const GRANTS_UI_BACKEND_ENDPOINT = config.get('session.cache.apiEndpoint')
 
+function logLockReleaseError(err, urlHref, ownerId, timeoutMs) {
+  if (err.name === 'AbortError') {
+    log(LogCodes.APPLICATION_LOCKS.RELEASE_TIMEOUT, {
+      ownerId,
+      timeoutMs
+    })
+  } else {
+    log(LogCodes.SYSTEM.EXTERNAL_API_ERROR, {
+      method: 'DELETE',
+      endpoint: urlHref,
+      service: 'grants-ui-backend',
+      identity: ownerId,
+      errorMessage: err.message
+    })
+  }
+}
+
 /**
  * Releases all application locks held by a given user via the grants-ui-backend API.
  *
@@ -61,8 +78,10 @@ export async function releaseAllApplicationLocksForOwnerFromApi({ ownerId }) {
       log(LogCodes.SYSTEM.EXTERNAL_API_ERROR, {
         method: 'DELETE',
         endpoint: url.href,
+        service: 'grants-ui-backend',
+        upstreamStatus: response.status,
         identity: ownerId,
-        errorMessage: `${response.status} - ${response.statusText}`
+        errorMessage: response.statusText
       })
       return { ok: false, releasedCount: 0 }
     }
@@ -74,19 +93,7 @@ export async function releaseAllApplicationLocksForOwnerFromApi({ ownerId }) {
     })
     return { ok: true, releasedCount: body.releasedCount ?? 0 }
   } catch (err) {
-    if (err.name === 'AbortError') {
-      debug(LogCodes.APPLICATION_LOCKS.RELEASE_TIMEOUT, {
-        ownerId,
-        timeoutMs
-      })
-    } else {
-      debug(LogCodes.SYSTEM.EXTERNAL_API_ERROR, {
-        method: 'DELETE',
-        endpoint: url.href,
-        identity: ownerId,
-        errorMessage: err.message
-      })
-    }
+    logLockReleaseError(err, url.href, ownerId, timeoutMs)
     return { ok: false, releasedCount: 0 }
   } finally {
     clearTimeout(timeoutId)
diff --git a/src/server/common/helpers/lock/application-lock.test.js b/src/server/common/helpers/lock/application-lock.test.js
index dd27ecbef..260fc35f4 100644
--- a/src/server/common/helpers/lock/application-lock.test.js
+++ b/src/server/common/helpers/lock/application-lock.test.js
@@ -19,7 +19,6 @@ vi.mock('./lock-token.js', () => ({
 
 let releaseAllApplicationLocksForOwnerFromApi
 let log
-let debug
 let LogCodes
 
 describe('releaseAllApplicationLocksForOwnerFromApi', () => {
@@ -37,7 +36,6 @@ describe('releaseAllApplicationLocksForOwnerFromApi', () => {
       releaseAllApplicationLocksForOwnerFromApi = helper.releaseAllApplicationLocksForOwnerFromApi
       const logModule = await import('~/src/server/common/helpers/logging/log.js')
       log = logModule.log
-      debug = logModule.debug
       LogCodes = logModule.LogCodes
       vi.clearAllMocks()
       createApiHeadersForGrantsUiBackend.mockReturnValue({ Authorization: 'Bearer token' })
@@ -85,7 +83,9 @@ describe('releaseAllApplicationLocksForOwnerFromApi', () => {
       expect(log).toHaveBeenCalledWith(
         LogCodes.SYSTEM.EXTERNAL_API_ERROR,
         expect.objectContaining({
-          errorMessage: '500 - Internal Server Error'
+          service: 'grants-ui-backend',
+          upstreamStatus: 500,
+          errorMessage: 'Internal Server Error'
         })
       )
     })
@@ -96,9 +96,10 @@ describe('releaseAllApplicationLocksForOwnerFromApi', () => {
       const result = await releaseAllApplicationLocksForOwnerFromApi({ ownerId })
 
       expect(result).toEqual({ ok: false, releasedCount: 0 })
-      expect(debug).toHaveBeenCalledWith(
+      expect(log).toHaveBeenCalledWith(
         LogCodes.SYSTEM.EXTERNAL_API_ERROR,
         expect.objectContaining({
+          service: 'grants-ui-backend',
           errorMessage: 'Network failure'
         })
       )
@@ -125,7 +126,7 @@ describe('releaseAllApplicationLocksForOwnerFromApi', () => {
 
       expect(result).toEqual({ ok: false, releasedCount: 0 })
 
-      expect(debug).toHaveBeenCalledWith(
+      expect(log).toHaveBeenCalledWith(
         LogCodes.APPLICATION_LOCKS.RELEASE_TIMEOUT,
         expect.objectContaining({
           ownerId
@@ -149,7 +150,6 @@ describe('releaseAllApplicationLocksForOwnerFromApi', () => {
 
       const logModule = await import('~/src/server/common/helpers/logging/log.js')
       log = logModule.log
-      debug = logModule.debug
 
       vi.clearAllMocks()
     })
diff --git a/src/server/common/helpers/logging/log-codes-definition.js b/src/server/common/helpers/logging/log-codes-definition.js
deleted file mode 100644
index 550159a36..000000000
--- a/src/server/common/helpers/logging/log-codes-definition.js
+++ /dev/null
@@ -1,507 +0,0 @@
-/**
- * @namespace LogTypes
- * @typedef {"info"|"warn"|"error"|"debug"} LogTypes.LogLevel
- *
- * @typedef { Object } LogCodesDefinition
- * @property {LogTypes.LogLevel} level - The log level (e.g., 'info', 'warn', 'error', 'debug').
- * @property {(messageOptions: Object) => string} messageFunc - A function that takes message options and returns a formatted log message string.
- */
-
-/**
- * @type {Object<string, Object<string, LogCodesDefinition>>}
- */
-export const LogCodes = {
-  AUTH: {
-    GENERIC_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Authentication error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
-    },
-    SIGN_IN_ATTEMPT: {
-      level: 'info',
-      messageFunc: (messageOptions) => `User sign-in attempt for user=${messageOptions.userId || 'unknown'}`
-    },
-    SIGN_IN_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `User sign-in successful for user=${messageOptions.userId}, organisation=${messageOptions.organisationId}`
-    },
-    SIGN_IN_FAILURE: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `User sign-in failed for user=${messageOptions.userId || 'unknown'}. Error: ${messageOptions.errorMessage}`
-    },
-    SIGN_OUT: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `User sign-out for user=${messageOptions.userId}, session=${messageOptions.sessionId}`
-    },
-    TOKEN_VERIFICATION_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Token verification successful for userCRN=${messageOptions.userId}, userSBI=${messageOptions.organisationId}`
-    },
-    TOKEN_VERIFICATION_FAILURE: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Token verification failed for user=${messageOptions.userId || 'unknown'}. Error: ${messageOptions.errorMessage}`
-    },
-    SESSION_EXPIRED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Session expired for user=${messageOptions.userId}, session=${messageOptions.sessionId}`
-    },
-    UNAUTHORIZED_ACCESS: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Unauthorized access attempt to path=${messageOptions.path} from user=${messageOptions.userId || 'unknown'}`
-    },
-    AUTH_DEBUG: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `Auth debug for path=${messageOptions.path}: isAuthenticated=${messageOptions.isAuthenticated}, strategy=${messageOptions.strategy}, mode=${messageOptions.mode}, hasCredentials=${messageOptions.hasCredentials}, hasToken=${messageOptions.hasToken}, hasProfile=${messageOptions.hasProfile}, userAgent=${messageOptions.userAgent}, referer=${messageOptions.referer}, queryParams=${JSON.stringify(messageOptions.queryParams)}, authError=${messageOptions.authError}`
-    },
-    WHITELIST_ACCESS_GRANTED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Whitelist access granted to path=${messageOptions.path} for user=${messageOptions.userId || 'unknown'}, sbi=${messageOptions.sbi || 'N/A'}: ${messageOptions.validationType || 'validation passed'}`
-    },
-    WHITELIST_ACCESS_DENIED_BOTH: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Whitelist access denied to path=${messageOptions.path}: Both CRN ${messageOptions.userId || 'unknown'} and SBI ${messageOptions.sbi || 'unknown'} failed validation`
-    },
-    WHITELIST_ACCESS_DENIED_CRN_PASSED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Whitelist access denied to path=${messageOptions.path}: CRN ${messageOptions.userId || 'unknown'} passed but SBI ${messageOptions.sbi || 'unknown'} failed validation`
-    },
-    WHITELIST_ACCESS_DENIED_SBI_PASSED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Whitelist access denied to path=${messageOptions.path}: SBI ${messageOptions.sbi || 'unknown'} passed but CRN ${messageOptions.userId || 'unknown'} failed validation`
-    },
-    CREDENTIALS_MISSING: {
-      level: 'error',
-      messageFunc: () => 'No credentials received from Bell OAuth provider'
-    },
-    TOKEN_MISSING: {
-      level: 'error',
-      messageFunc: () => 'No token received from Defra Identity'
-    },
-    INVALID_STATE: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Invalid OAuth state provided | reason=${messageOptions.reason} | storedStatePresent=${messageOptions.storedStatePresent}`
-    }
-  },
-  FORMS: {
-    FORM_LOAD: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Form loaded: ${messageOptions.formName} for user=${messageOptions.userId || 'unknown'}`
-    },
-    FORM_SUBMIT: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Form submitted: ${messageOptions.formName} by user=${messageOptions.userId || 'unknown'}`
-    },
-    FORM_VALIDATION_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Form validation error in ${messageOptions.formName}: ${messageOptions.errorMessage}`
-    },
-    FORM_VALIDATION_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) => `Form validation successful for ${messageOptions.formName}`
-    },
-    FORM_PROCESSING_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Form processing error for ${messageOptions.formName}: ${messageOptions.errorMessage}`
-    },
-    FORM_SAVE: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Form saved: ${messageOptions.formName} for user=${messageOptions.userId || 'unknown'}`
-    },
-    SLUG_STORED: {
-      level: 'debug',
-      messageFunc: (messageOptions) => `${messageOptions.controller}: Storing slug in context: ${messageOptions.slug}`
-    },
-    SLUG_RESOLVED: {
-      level: 'debug',
-      messageFunc: (messageOptions) => `${messageOptions.controller}: ${messageOptions.message}`
-    }
-  },
-  SUBMISSION: {
-    SUBMISSION_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Grant submission successful for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}`
-    },
-    SUBMISSION_COMPLETED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Form submission completed for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}, fields=${messageOptions.numberOfFields || 0}, status=${messageOptions.status}`
-    },
-    SUBMISSION_FAILURE: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Grant submission failed for grantType=${messageOptions.grantType}, userCrn=${messageOptions.userCrn}, userSbi=${messageOptions.userSbi}, error=${messageOptions.errorMessage}`
-    },
-    SUBMISSION_VALIDATION_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Submission validation error for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}, validationId=${messageOptions.validationId}`
-    },
-    SUBMISSION_PAYLOAD_LOG: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `Submission payload for grantType=${messageOptions.grantType}:\n${JSON.stringify(messageOptions.payload, null, 2)}`
-    },
-    SUBMISSION_REDIRECT_FAILURE: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Submission redirect failure for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}. Error: ${messageOptions.errorMessage}`
-    },
-    VALIDATOR_NOT_FOUND: {
-      level: 'error',
-      messageFunc: (messageOptions) => `No validator found for grantType=${messageOptions.grantType}`
-    },
-    APPLICATION_STATUS_UPDATED: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `${messageOptions.controller}: Application status updated to ${messageOptions.status}`
-    },
-    SUBMISSION_PROCESSING: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `${messageOptions.controller}: Processing form submission, path=${messageOptions.path}`
-    },
-    SUBMISSION_REDIRECT: {
-      level: 'debug',
-      messageFunc: (messageOptions) => `${messageOptions.controller}: Redirecting to ${messageOptions.redirectPath}`
-    }
-  },
-  DECLARATION: {
-    DECLARATION_LOAD: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Declaration page loaded for user=${messageOptions.userId}, grantType=${messageOptions.grantType}`
-    },
-    DECLARATION_ACCEPTED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Declaration accepted by user=${messageOptions.userId}, grantType=${messageOptions.grantType}`
-    },
-    DECLARATION_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Declaration processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
-    }
-  },
-  CONFIRMATION: {
-    CONFIRMATION_LOAD: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Confirmation page loaded for user=${messageOptions.userId}, grantType=${messageOptions.grantType}`
-    },
-    CONFIRMATION_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Confirmation processed successfully for user=${messageOptions.userId}, referenceNumber=${messageOptions.referenceNumber}`
-    },
-    CONFIRMATION_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Confirmation processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
-    },
-    SUBMITTED_STATUS_RETRIEVED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `${messageOptions.controller}: Retrieved submitted status for referenceNumber=${messageOptions.referenceNumber}`
-    }
-  },
-  LAND_GRANTS: {
-    LAND_GRANT_APPLICATION_STARTED: {
-      level: 'info',
-      messageFunc: (messageOptions) => `Land grant application started for user=${messageOptions.userId}`
-    },
-    LAND_GRANT_APPLICATION_SUBMITTED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Land grant application submitted for user=${messageOptions.userId}, referenceNumber=${messageOptions.referenceNumber}`
-    },
-    LAND_GRANT_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Land grant processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
-    },
-    NO_LAND_PARCELS_FOUND: {
-      level: 'warn',
-      messageFunc: (messageOptions) => `No land parcels found for sbi=${messageOptions.sbi}`
-    },
-    NO_ACTIONS_FOUND: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `No actions found | parcelId: ${messageOptions.parcelId} | sheetId: ${messageOptions.sheetId}`
-    },
-    VALIDATE_APPLICATION_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Error validating application: ${messageOptions.errorMessage} | parcelId: ${messageOptions.parcelId} | sheetId: ${messageOptions.sheetId}`
-    },
-    FETCH_ACTIONS_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Error fetching actions: ${messageOptions.errorMessage} | sbi: ${messageOptions.sbi} | parcelId: ${messageOptions.parcelId} | sheetId: ${messageOptions.sheetId}`
-    },
-    FARM_DETAILS_MISSING_FIELDS: {
-      level: 'warn',
-      messageFunc: (messageOptions) =>
-        `Missing farm contact details for sbi: ${messageOptions.sbi} | fields: ${messageOptions.missingFields.join(', ')}`
-    },
-    UNAUTHORISED_PARCEL: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Land parcel doesn't belong to sbi=${messageOptions.sbi} | selectedLandParcel: ${messageOptions.selectedLandParcel} | landParcelsForSbi=${JSON.stringify(messageOptions.landParcelsForSbi)}`
-    },
-    API_REQUEST: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Land Grants API request | endpoint: ${messageOptions.endpoint} | url: ${messageOptions.url}`
-    }
-  },
-  WOODLAND: {
-    VALIDATE_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) => `Woodland validation error: ${messageOptions.errorMessage}`
-    }
-  },
-  AGREEMENTS: {
-    AGREEMENT_LOAD: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Agreement loaded for user=${messageOptions.userId}, agreementType=${messageOptions.agreementType}`
-    },
-    AGREEMENT_ACCEPTED: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Agreement accepted by user=${messageOptions.userId}, agreementType=${messageOptions.agreementType}`
-    },
-    AGREEMENT_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Agreement processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
-    },
-    PROXY_RESPONSE_ERROR: {
-      level: 'error',
-      messageFunc: () => 'Proxy response is undefined. Possible upstream error or misconfiguration.'
-    }
-  },
-  COOKIES: {
-    PAGE_LOAD: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Cookies page loaded: returnUrl=${messageOptions.returnUrl}, referer=${messageOptions.referer}`
-    }
-  },
-
-  RESOURCE_NOT_FOUND: {
-    FORM_NOT_FOUND: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Form not found: slug=${messageOptions.slug}, userId=${messageOptions.userId || 'anonymous'}, sbi=${messageOptions.sbi || 'unknown'}, reason=${messageOptions.reason || 'not_found'}, environment=${messageOptions.environment || 'unknown'}, referer=${messageOptions.referer || 'none'}`
-    },
-    PAGE_NOT_FOUND: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Page not found: path=${messageOptions.path}, userId=${messageOptions.userId || 'anonymous'}, sbi=${messageOptions.sbi || 'unknown'}, referer=${messageOptions.referer || 'none'}, userAgent=${messageOptions.userAgent || 'unknown'}`
-    }
-  },
-  APPLICATION_LOCKS: {
-    RELEASE_SKIPPED: {
-      level: 'debug',
-      messageFunc: ({ ownerId, reason }) => `Application locks release skipped | ownerId=${ownerId} | reason=${reason}`
-    },
-    RELEASE_ATTEMPTED: {
-      level: 'debug',
-      messageFunc: ({ ownerId }) => `Attempting application locks release | ownerId=${ownerId}`
-    },
-    RELEASE_SUCCEEDED: {
-      level: 'debug',
-      messageFunc: ({ ownerId, releasedCount }) =>
-        `Application locks released | ownerId=${ownerId} | releasedCount=${releasedCount}`
-    },
-    RELEASE_TIMEOUT: {
-      level: 'warn',
-      messageFunc: ({ ownerId, timeoutMs }) =>
-        `Application locks release timed out | ownerId=${ownerId} | timeoutMs=${timeoutMs}`
-    },
-    RELEASE_FAILED: {
-      level: 'error',
-      messageFunc: ({ ownerId, errorName, errorMessage }) =>
-        `Failed to release application locks | ownerId=${ownerId} | errorName=${errorName} | errorMessage=${errorMessage}`
-    }
-  },
-  PRINT_APPLICATION: {
-    SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) => `Print application viewed for referenceNumber=${messageOptions.referenceNumber}`
-    },
-    ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Print application error for user=${messageOptions.userId}, slug=${messageOptions.slug}: ${messageOptions.errorMessage}`
-    }
-  },
-  SYSTEM: {
-    GENERIC_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) => `An error occurred: ${messageOptions.errorMessage}`
-    },
-    VIEW_DEBUG: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `View path debug: currentFile=${messageOptions.currentFilePath}, isBuilt=${messageOptions.isRunningBuiltCode}, basePath=${messageOptions.basePath}, workingDir=${messageOptions.processWorkingDir}, pathsResolved=${messageOptions.resolvedViewPaths?.length || 0}`
-    },
-    VIEW_PATH_CHECK: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `View path ${messageOptions.index}: path=${messageOptions.path}, exists=${messageOptions.exists}, isAbsolute=${messageOptions.isAbsolute}`
-    },
-    ENV_CONFIG_DEBUG: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `Environment configuration: ${messageOptions.configType} - ${JSON.stringify(messageOptions.configValues)}`
-    },
-    SERVER_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) => `Server error occurred: ${messageOptions.errorMessage}`
-    },
-    STARTUP_PHASE: {
-      level: 'info',
-      messageFunc: (messageOptions) => `Startup phase: ${messageOptions.phase} - ${messageOptions.status}`
-    },
-    PLUGIN_REGISTRATION: {
-      level: 'debug',
-      messageFunc: (messageOptions) => `Plugin registration: ${messageOptions.pluginName} - ${messageOptions.status}`
-    },
-    SYSTEM_STARTUP: {
-      level: 'info',
-      messageFunc: (messageOptions) => `System startup completed on port=${messageOptions.port}`
-    },
-    SYSTEM_SHUTDOWN: {
-      level: 'info',
-      messageFunc: () => 'System shutdown initiated'
-    },
-    EXTERNAL_API_CALL: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `External API call to ${messageOptions.endpoint} for user=${messageOptions.userId || 'unknown'}`
-    },
-    EXTERNAL_API_CALL_DEBUG: {
-      level: 'debug',
-      messageFunc: (messageOptions) =>
-        `External ${messageOptions.method} to ${new URL(messageOptions.endpoint).pathname} (${messageOptions.identity || 'unknown'})`
-    },
-    EXTERNAL_API_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `External API error for ${messageOptions.endpoint}: ${messageOptions.errorMessage}`
-    },
-    GAS_ACTION_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Error invoking GAS action ${messageOptions.action} for grant ${messageOptions.grantCode}: ${messageOptions.errorMessage}`
-    },
-    BACKEND_AUTH_CONFIG_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Backend auth configuration invalid | missingKeys=${messageOptions.missingKeys?.join(', ') || 'unknown'}`
-    },
-    RELATIONSHIP_PARSE_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `extractFarmDetails: Invalid relationship format | relationships="${messageOptions.relationships}" | reason=${messageOptions.reason}`
-    },
-    CONFIG_MISSING: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Missing required configuration: ${messageOptions?.missing?.join(', ') || 'unknown'}`
-    },
-    CONFIG_INVALID: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Invalid configuration, key "${messageOptions.key}" is missing or invalid: ${messageOptions.value}`
-    },
-    WHITELIST_CONFIG_INCOMPLETE: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Incomplete whitelist configuration in form "${messageOptions.formName}" | present=${messageOptions.presentVar} | missing=${messageOptions.missingVar}`
-    },
-    CRN_ENV_VAR_MISSING: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `CRN whitelist environment variable "${messageOptions.envVar}" missing for form "${messageOptions.formName}"`
-    },
-    SBI_ENV_VAR_MISSING: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `SBI whitelist environment variable "${messageOptions.envVar}" missing for form "${messageOptions.formName}"`
-    },
-    INVALID_REDIRECT_RULES: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Invalid redirect rules in form "${messageOptions.formName}" | reason=${messageOptions.reason}`
-    },
-    CONSOLIDATED_VIEW_API_ERROR: {
-      level: 'error',
-      messageFunc: (messageOptions) => {
-        const base = `Unexpected error fetching business data from Consolidated View API | sbi=${messageOptions.sbi || 'unknown'} | status=${messageOptions.statusCode || 'unknown'} | error=${messageOptions.errorMessage}`
-        return messageOptions.responseBody ? `${base} | responseBody=${messageOptions.responseBody}` : base
-      }
-    },
-    CONSOLIDATED_VIEW_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Consolidated View API request successful | sbi=${messageOptions.sbi || 'unknown'}`
-    },
-    CONSOLIDATED_VIEW_PARTIAL_SUCCESS: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Partial success from Consolidated View API | sbi=${messageOptions.sbi || 'unknown'} | failedPaths=${messageOptions.failedPaths} | status=${messageOptions.statusCode || 'unknown'}`
-    },
-    CONSOLIDATED_VIEW_ADDRESS_FORMAT: {
-      level: 'info',
-      messageFunc: (messageOptions) =>
-        `Address format for sbi=${messageOptions.sbi} is ${messageOptions.uprn ? 'structured' : 'unstructured'}, uprn=${messageOptions.uprn || 'not set'}`
-    },
-    SESSION_STATE_CLEAR_FAILED: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Failed to clear application state for slug=${messageOptions.slug}, sessionKey=${messageOptions.sessionKey}, error=${messageOptions.errorMessage}`
-    },
-    SESSION_STATE_KEY_PARSE_FAILED: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Failed to parse session key: error=${messageOptions.errorMessage}, path=${messageOptions.requestPath}`
-    },
-    SESSION_STATE_FETCH_FAILED: {
-      level: 'error',
-      messageFunc: (messageOptions) =>
-        `Failed to fetch saved state: sessionKey=${messageOptions.sessionKey}, error=${messageOptions.errorMessage}, path=${messageOptions.requestPath}`
-    },
-    RATE_LIMIT_EXCEEDED: {
-      level: 'warn',
-      messageFunc: (messageOptions) =>
-        `Rate limit exceeded: path=${messageOptions.path}, ip=${messageOptions.ip || 'unknown'}, userId=${messageOptions.userId || 'anonymous'}, userAgent=${messageOptions.userAgent || 'unknown'}`
-    },
-    STATE_SIZE_EXCEEDED: {
-      level: 'warn',
-      messageFunc: (messageOptions) =>
-        `State payload size ${messageOptions.size} bytes exceeds limit of ${messageOptions.limit} bytes for sessionKey=${messageOptions.sessionKey}`
-    }
-  }
-}
diff --git a/src/server/common/helpers/logging/log-codes.js b/src/server/common/helpers/logging/log-codes.js
index 63d3be26d..e1fea0c6d 100644
--- a/src/server/common/helpers/logging/log-codes.js
+++ b/src/server/common/helpers/logging/log-codes.js
@@ -1,5 +1,5 @@
 import { validateLogCode } from './log-code-validator.js'
-import { LogCodes } from './log-codes-definition.js'
+import { LogCodes } from './log-codes/definition.js'
 
 // Re-export LogCodes from the definition file
 export { LogCodes }
diff --git a/src/server/common/helpers/logging/log-codes.test.js b/src/server/common/helpers/logging/log-codes.test.js
index 40b59d14c..dfcf640dc 100644
--- a/src/server/common/helpers/logging/log-codes.test.js
+++ b/src/server/common/helpers/logging/log-codes.test.js
@@ -143,6 +143,12 @@ describe('LogCodes', () => {
         'error',
         { errorMessage: TEST_ERRORS.INVALID_TOKEN },
         `Token verification failed for user=unknown. Error: ${TEST_ERRORS.INVALID_TOKEN}`
+      ],
+      [
+        'GENERIC_ERROR',
+        'error',
+        { userId: TEST_USER_IDS.DEFAULT, errorMessage: TEST_ERRORS.INVALID_CREDENTIALS },
+        `Authentication error for user=${TEST_USER_IDS.DEFAULT}: ${TEST_ERRORS.INVALID_CREDENTIALS}`
       ]
     ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
       assertLogCode('AUTH', logCodeName, expectedLevel, testParams, expectedMessage)
@@ -300,6 +306,18 @@ describe('LogCodes', () => {
         'info',
         { formName: TEST_FORM_NAMES.DECLARATION },
         `Form saved: ${TEST_FORM_NAMES.DECLARATION} for user=unknown`
+      ],
+      [
+        'SLUG_STORED',
+        'debug',
+        { controller: 'DeclarationController', slug: 'example-grant' },
+        'DeclarationController: Storing slug in context: example-grant'
+      ],
+      [
+        'SLUG_RESOLVED',
+        'debug',
+        { controller: 'DeclarationController', message: 'Resolved slug from context' },
+        'DeclarationController: Resolved slug from context'
       ]
     ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
       assertLogCode('FORMS', logCodeName, expectedLevel, testParams, expectedMessage)
@@ -519,6 +537,18 @@ describe('LogCodes', () => {
         'info',
         { endpoint: '/api/v2/parcels', url: 'https://land-grants-api/api/v2/parcels' },
         'Land Grants API request | endpoint: /api/v2/parcels | url: https://land-grants-api/api/v2/parcels'
+      ],
+      [
+        'FARM_DETAILS_MISSING_FIELDS',
+        'warn',
+        { sbi: TEST_SBI.DEFAULT, missingFields: ['email', 'telephone'] },
+        `Missing farm contact details for sbi: ${TEST_SBI.DEFAULT} | fields: email, telephone`
+      ],
+      [
+        'FARM_DETAILS_MISSING_FIELDS with single field',
+        'warn',
+        { sbi: TEST_SBI.DEFAULT, missingFields: ['email'] },
+        `Missing farm contact details for sbi: ${TEST_SBI.DEFAULT} | fields: email`
       ]
     ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
       assertLogCode('LAND_GRANTS', logCodeName, expectedLevel, testParams, expectedMessage)
@@ -544,12 +574,63 @@ describe('LogCodes', () => {
         'error',
         { userId: TEST_USER_IDS.DEFAULT, errorMessage: TEST_ERRORS.PROCESSING_FAILED },
         `Agreement processing error for user=${TEST_USER_IDS.DEFAULT}: ${TEST_ERRORS.PROCESSING_FAILED}`
-      ]
+      ],
+      ['PROXY_RESPONSE_ERROR', 'error', {}, 'Proxy response is undefined. Possible upstream error or misconfiguration.']
     ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
       assertLogCode('AGREEMENTS', logCodeName, expectedLevel, testParams, expectedMessage)
     })
   })
 
+  describe('APPLICATION_LOCKS log codes', () => {
+    it.each([
+      [
+        'RELEASE_SKIPPED',
+        'debug',
+        { ownerId: 'session-abc', reason: 'no-owner' },
+        'Application locks release skipped | ownerId=session-abc | reason=no-owner'
+      ],
+      [
+        'RELEASE_ATTEMPTED',
+        'debug',
+        { ownerId: 'session-abc' },
+        'Attempting application locks release | ownerId=session-abc'
+      ],
+      [
+        'RELEASE_SUCCEEDED',
+        'debug',
+        { ownerId: 'session-abc', releasedCount: 3 },
+        'Application locks released | ownerId=session-abc | releasedCount=3'
+      ],
+      [
+        'RELEASE_TIMEOUT',
+        'warn',
+        { ownerId: 'session-abc', timeoutMs: 5000 },
+        'Application locks release timed out | ownerId=session-abc | timeoutMs=5000'
+      ],
+      [
+        'RELEASE_FAILED',
+        'error',
+        { ownerId: 'session-abc', errorName: 'TimeoutError', errorMessage: 'connection lost' },
+        'Failed to release application locks | ownerId=session-abc | errorName=TimeoutError | errorMessage=connection lost'
+      ]
+    ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
+      assertLogCode('APPLICATION_LOCKS', logCodeName, expectedLevel, testParams, expectedMessage)
+    })
+  })
+
+  describe('WOODLAND log codes', () => {
+    it.each([
+      [
+        'VALIDATE_ERROR',
+        'error',
+        { errorMessage: 'Invalid woodland data' },
+        'Woodland validation error: Invalid woodland data'
+      ]
+    ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
+      assertLogCode('WOODLAND', logCodeName, expectedLevel, testParams, expectedMessage)
+    })
+  })
+
   describe('COOKIES log codes', () => {
     it.each([
       [
@@ -634,6 +715,18 @@ describe('LogCodes', () => {
         { errorMessage: TEST_ERRORS.DATABASE_ERROR },
         `Server error occurred: ${TEST_ERRORS.DATABASE_ERROR}`
       ],
+      [
+        'SERVER_ERROR with upstreamStatus',
+        'error',
+        { errorMessage: TEST_ERRORS.DATABASE_ERROR, upstreamStatus: 502 },
+        `Server error occurred: ${TEST_ERRORS.DATABASE_ERROR} | upstreamStatus=502`
+      ],
+      [
+        'SERVER_ERROR with null upstreamStatus is omitted',
+        'error',
+        { errorMessage: TEST_ERRORS.DATABASE_ERROR, upstreamStatus: null },
+        `Server error occurred: ${TEST_ERRORS.DATABASE_ERROR}`
+      ],
       [
         'SYSTEM_STARTUP',
         'info',
@@ -664,6 +757,29 @@ describe('LogCodes', () => {
         { endpoint: TEST_ENDPOINTS.API_GRANTS, errorMessage: TEST_ERRORS.CONNECTION_FAILED },
         `External API error for ${TEST_ENDPOINTS.API_GRANTS}: ${TEST_ERRORS.CONNECTION_FAILED}`
       ],
+      [
+        'EXTERNAL_API_ERROR with service and upstreamStatus',
+        'error',
+        {
+          endpoint: TEST_ENDPOINTS.API_GRANTS,
+          errorMessage: TEST_ERRORS.CONNECTION_FAILED,
+          service: 'grants-ui-backend',
+          upstreamStatus: 502
+        },
+        `External API error for ${TEST_ENDPOINTS.API_GRANTS} | service=grants-ui-backend | upstreamStatus=502: ${TEST_ERRORS.CONNECTION_FAILED}`
+      ],
+      [
+        'EXTERNAL_API_ERROR with attempts after retry exhaustion',
+        'error',
+        {
+          endpoint: TEST_ENDPOINTS.API_GRANTS,
+          errorMessage: TEST_ERRORS.CONNECTION_FAILED,
+          service: 'grants-ui-backend',
+          upstreamStatus: 502,
+          attempts: 3
+        },
+        `External API error for ${TEST_ENDPOINTS.API_GRANTS} | service=grants-ui-backend | upstreamStatus=502 | attempts=3: ${TEST_ERRORS.CONNECTION_FAILED}`
+      ],
       [
         'GAS_ACTION_ERROR',
         'error',
@@ -811,6 +927,77 @@ describe('LogCodes', () => {
         'error',
         { errorMessage: 'Connection failed' },
         'Unexpected error fetching business data from Consolidated View API | sbi=unknown | status=unknown | error=Connection failed'
+      ],
+      [
+        'CONSOLIDATED_VIEW_API_ERROR with statusCode and responseBody',
+        'error',
+        {
+          sbi: TEST_SBI.DEFAULT,
+          statusCode: 503,
+          errorMessage: 'Service Unavailable',
+          responseBody: '{"error":"upstream"}'
+        },
+        `Unexpected error fetching business data from Consolidated View API | sbi=${TEST_SBI.DEFAULT} | status=503 | error=Service Unavailable | responseBody={"error":"upstream"}`
+      ],
+      [
+        'GENERIC_ERROR',
+        'error',
+        { errorMessage: TEST_ERRORS.DATABASE_ERROR },
+        `An error occurred: ${TEST_ERRORS.DATABASE_ERROR}`
+      ],
+      [
+        'CONFIG_INVALID',
+        'error',
+        { key: 'apiUrl', value: 'not-a-url' },
+        'Invalid configuration, key "apiUrl" is missing or invalid: not-a-url'
+      ],
+      [
+        'CONSOLIDATED_VIEW_SUCCESS',
+        'info',
+        { sbi: TEST_SBI.DEFAULT },
+        `Consolidated View API request successful | sbi=${TEST_SBI.DEFAULT}`
+      ],
+      ['CONSOLIDATED_VIEW_SUCCESS with fallback', 'info', {}, 'Consolidated View API request successful | sbi=unknown'],
+      [
+        'CONSOLIDATED_VIEW_PARTIAL_SUCCESS',
+        'info',
+        { sbi: TEST_SBI.DEFAULT, failedPaths: 'address,phone', statusCode: 207 },
+        `Partial success from Consolidated View API | sbi=${TEST_SBI.DEFAULT} | failedPaths=address,phone | status=207`
+      ],
+      [
+        'CONSOLIDATED_VIEW_PARTIAL_SUCCESS with fallbacks',
+        'info',
+        { failedPaths: 'address' },
+        'Partial success from Consolidated View API | sbi=unknown | failedPaths=address | status=unknown'
+      ],
+      [
+        'CONSOLIDATED_VIEW_ADDRESS_FORMAT structured',
+        'info',
+        { sbi: TEST_SBI.DEFAULT, uprn: '12345' },
+        `Address format for sbi=${TEST_SBI.DEFAULT} is structured, uprn=12345`
+      ],
+      [
+        'CONSOLIDATED_VIEW_ADDRESS_FORMAT unstructured',
+        'info',
+        { sbi: TEST_SBI.DEFAULT },
+        `Address format for sbi=${TEST_SBI.DEFAULT} is unstructured, uprn=not set`
+      ],
+      [
+        'RATE_LIMIT_EXCEEDED',
+        'warn',
+        {
+          path: TEST_PATHS.EXAMPLE_GRANT,
+          ip: '127.0.0.1',
+          userId: TEST_USER_IDS.DEFAULT,
+          userAgent: 'Mozilla/5.0'
+        },
+        `Rate limit exceeded: path=${TEST_PATHS.EXAMPLE_GRANT}, ip=127.0.0.1, userId=${TEST_USER_IDS.DEFAULT}, userAgent=Mozilla/5.0`
+      ],
+      [
+        'RATE_LIMIT_EXCEEDED with fallbacks',
+        'warn',
+        { path: TEST_PATHS.EXAMPLE_GRANT },
+        `Rate limit exceeded: path=${TEST_PATHS.EXAMPLE_GRANT}, ip=unknown, userId=anonymous, userAgent=unknown`
       ]
     ])('should have valid %s log code', (logCodeName, expectedLevel, testParams, expectedMessage) => {
       assertLogCode('SYSTEM', logCodeName, expectedLevel, testParams, expectedMessage)
diff --git a/src/server/common/helpers/logging/log-codes/agreements.js b/src/server/common/helpers/logging/log-codes/agreements.js
new file mode 100644
index 000000000..8ccc6c397
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/agreements.js
@@ -0,0 +1,24 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const AGREEMENTS = {
+  AGREEMENT_LOAD: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Agreement loaded for user=${messageOptions.userId}, agreementType=${messageOptions.agreementType}`
+  },
+  AGREEMENT_ACCEPTED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Agreement accepted by user=${messageOptions.userId}, agreementType=${messageOptions.agreementType}`
+  },
+  AGREEMENT_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Agreement processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
+  },
+  PROXY_RESPONSE_ERROR: {
+    level: 'error',
+    messageFunc: () => 'Proxy response is undefined. Possible upstream error or misconfiguration.'
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/application-locks.js b/src/server/common/helpers/logging/log-codes/application-locks.js
new file mode 100644
index 000000000..8e8507ac0
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/application-locks.js
@@ -0,0 +1,28 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const APPLICATION_LOCKS = {
+  RELEASE_SKIPPED: {
+    level: 'debug',
+    messageFunc: ({ ownerId, reason }) => `Application locks release skipped | ownerId=${ownerId} | reason=${reason}`
+  },
+  RELEASE_ATTEMPTED: {
+    level: 'debug',
+    messageFunc: ({ ownerId }) => `Attempting application locks release | ownerId=${ownerId}`
+  },
+  RELEASE_SUCCEEDED: {
+    level: 'debug',
+    messageFunc: ({ ownerId, releasedCount }) =>
+      `Application locks released | ownerId=${ownerId} | releasedCount=${releasedCount}`
+  },
+  RELEASE_TIMEOUT: {
+    level: 'warn',
+    messageFunc: ({ ownerId, timeoutMs }) =>
+      `Application locks release timed out | ownerId=${ownerId} | timeoutMs=${timeoutMs}`
+  },
+  RELEASE_FAILED: {
+    level: 'error',
+    messageFunc: ({ ownerId, errorName, errorMessage }) =>
+      `Failed to release application locks | ownerId=${ownerId} | errorName=${errorName} | errorMessage=${errorMessage}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/auth.js b/src/server/common/helpers/logging/log-codes/auth.js
new file mode 100644
index 000000000..9f26b6e95
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/auth.js
@@ -0,0 +1,87 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const AUTH = {
+  GENERIC_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Authentication error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
+  },
+  SIGN_IN_ATTEMPT: {
+    level: 'info',
+    messageFunc: (messageOptions) => `User sign-in attempt for user=${messageOptions.userId || 'unknown'}`
+  },
+  SIGN_IN_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `User sign-in successful for user=${messageOptions.userId}, organisation=${messageOptions.organisationId}`
+  },
+  SIGN_IN_FAILURE: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `User sign-in failed for user=${messageOptions.userId || 'unknown'}. Error: ${messageOptions.errorMessage}`
+  },
+  SIGN_OUT: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `User sign-out for user=${messageOptions.userId}, session=${messageOptions.sessionId}`
+  },
+  TOKEN_VERIFICATION_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Token verification successful for userCRN=${messageOptions.userId}, userSBI=${messageOptions.organisationId}`
+  },
+  TOKEN_VERIFICATION_FAILURE: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Token verification failed for user=${messageOptions.userId || 'unknown'}. Error: ${messageOptions.errorMessage}`
+  },
+  SESSION_EXPIRED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Session expired for user=${messageOptions.userId}, session=${messageOptions.sessionId}`
+  },
+  UNAUTHORIZED_ACCESS: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Unauthorized access attempt to path=${messageOptions.path} from user=${messageOptions.userId || 'unknown'}`
+  },
+  AUTH_DEBUG: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `Auth debug for path=${messageOptions.path}: isAuthenticated=${messageOptions.isAuthenticated}, strategy=${messageOptions.strategy}, mode=${messageOptions.mode}, hasCredentials=${messageOptions.hasCredentials}, hasToken=${messageOptions.hasToken}, hasProfile=${messageOptions.hasProfile}, userAgent=${messageOptions.userAgent}, referer=${messageOptions.referer}, queryParams=${JSON.stringify(messageOptions.queryParams)}, authError=${messageOptions.authError}`
+  },
+  WHITELIST_ACCESS_GRANTED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Whitelist access granted to path=${messageOptions.path} for user=${messageOptions.userId || 'unknown'}, sbi=${messageOptions.sbi || 'N/A'}: ${messageOptions.validationType || 'validation passed'}`
+  },
+  WHITELIST_ACCESS_DENIED_BOTH: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Whitelist access denied to path=${messageOptions.path}: Both CRN ${messageOptions.userId || 'unknown'} and SBI ${messageOptions.sbi || 'unknown'} failed validation`
+  },
+  WHITELIST_ACCESS_DENIED_CRN_PASSED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Whitelist access denied to path=${messageOptions.path}: CRN ${messageOptions.userId || 'unknown'} passed but SBI ${messageOptions.sbi || 'unknown'} failed validation`
+  },
+  WHITELIST_ACCESS_DENIED_SBI_PASSED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Whitelist access denied to path=${messageOptions.path}: SBI ${messageOptions.sbi || 'unknown'} passed but CRN ${messageOptions.userId || 'unknown'} failed validation`
+  },
+  CREDENTIALS_MISSING: {
+    level: 'error',
+    messageFunc: () => 'No credentials received from Bell OAuth provider'
+  },
+  TOKEN_MISSING: {
+    level: 'error',
+    messageFunc: () => 'No token received from Defra Identity'
+  },
+  INVALID_STATE: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Invalid OAuth state provided | reason=${messageOptions.reason} | storedStatePresent=${messageOptions.storedStatePresent}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/confirmation.js b/src/server/common/helpers/logging/log-codes/confirmation.js
new file mode 100644
index 000000000..5cc8d1176
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/confirmation.js
@@ -0,0 +1,25 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const CONFIRMATION = {
+  CONFIRMATION_LOAD: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Confirmation page loaded for user=${messageOptions.userId}, grantType=${messageOptions.grantType}`
+  },
+  CONFIRMATION_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Confirmation processed successfully for user=${messageOptions.userId}, referenceNumber=${messageOptions.referenceNumber}`
+  },
+  CONFIRMATION_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Confirmation processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
+  },
+  SUBMITTED_STATUS_RETRIEVED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `${messageOptions.controller}: Retrieved submitted status for referenceNumber=${messageOptions.referenceNumber}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/cookies.js b/src/server/common/helpers/logging/log-codes/cookies.js
new file mode 100644
index 000000000..c045ecefd
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/cookies.js
@@ -0,0 +1,10 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const COOKIES = {
+  PAGE_LOAD: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Cookies page loaded: returnUrl=${messageOptions.returnUrl}, referer=${messageOptions.referer}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/declaration.js b/src/server/common/helpers/logging/log-codes/declaration.js
new file mode 100644
index 000000000..c2a07a720
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/declaration.js
@@ -0,0 +1,20 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const DECLARATION = {
+  DECLARATION_LOAD: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Declaration page loaded for user=${messageOptions.userId}, grantType=${messageOptions.grantType}`
+  },
+  DECLARATION_ACCEPTED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Declaration accepted by user=${messageOptions.userId}, grantType=${messageOptions.grantType}`
+  },
+  DECLARATION_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Declaration processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/definition.js b/src/server/common/helpers/logging/log-codes/definition.js
new file mode 100644
index 000000000..571a067b0
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/definition.js
@@ -0,0 +1,41 @@
+import { AUTH } from './auth.js'
+import { FORMS } from './forms.js'
+import { SUBMISSION } from './submission.js'
+import { DECLARATION } from './declaration.js'
+import { CONFIRMATION } from './confirmation.js'
+import { LAND_GRANTS } from './land-grants.js'
+import { WOODLAND } from './woodland.js'
+import { AGREEMENTS } from './agreements.js'
+import { COOKIES } from './cookies.js'
+import { RESOURCE_NOT_FOUND } from './resource-not-found.js'
+import { APPLICATION_LOCKS } from './application-locks.js'
+import { PRINT_APPLICATION } from './print-application.js'
+import { SYSTEM } from './system.js'
+
+/**
+ * @namespace LogTypes
+ * @typedef {"info"|"warn"|"error"|"debug"} LogTypes.LogLevel
+ *
+ * @typedef {Object} LogCodesDefinition
+ * @property {LogTypes.LogLevel} level - The log level (e.g., 'info', 'warn', 'error', 'debug').
+ * @property {(messageOptions: Record<string, any>) => string} messageFunc - A function that takes message options. Each log code reads its own per-call fields, so the bag is intentionally loose; tightening to `unknown` breaks legitimate per-code field access (e.g. `.missingFields.join()`, `new URL(...)`).
+ */
+
+/**
+ * @type {Record<string, Record<string, LogCodesDefinition>>}
+ */
+export const LogCodes = {
+  AUTH,
+  FORMS,
+  SUBMISSION,
+  DECLARATION,
+  CONFIRMATION,
+  LAND_GRANTS,
+  WOODLAND,
+  AGREEMENTS,
+  COOKIES,
+  RESOURCE_NOT_FOUND,
+  APPLICATION_LOCKS,
+  PRINT_APPLICATION,
+  SYSTEM
+}
diff --git a/src/server/common/helpers/logging/log-codes/forms.js b/src/server/common/helpers/logging/log-codes/forms.js
new file mode 100644
index 000000000..8cea0a288
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/forms.js
@@ -0,0 +1,42 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const FORMS = {
+  FORM_LOAD: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Form loaded: ${messageOptions.formName} for user=${messageOptions.userId || 'unknown'}`
+  },
+  FORM_SUBMIT: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Form submitted: ${messageOptions.formName} by user=${messageOptions.userId || 'unknown'}`
+  },
+  FORM_VALIDATION_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Form validation error in ${messageOptions.formName}: ${messageOptions.errorMessage}`
+  },
+  FORM_VALIDATION_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) => `Form validation successful for ${messageOptions.formName}`
+  },
+  FORM_PROCESSING_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Form processing error for ${messageOptions.formName}: ${messageOptions.errorMessage}`
+  },
+  FORM_SAVE: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Form saved: ${messageOptions.formName} for user=${messageOptions.userId || 'unknown'}`
+  },
+  SLUG_STORED: {
+    level: 'debug',
+    messageFunc: (messageOptions) => `${messageOptions.controller}: Storing slug in context: ${messageOptions.slug}`
+  },
+  SLUG_RESOLVED: {
+    level: 'debug',
+    messageFunc: (messageOptions) => `${messageOptions.controller}: ${messageOptions.message}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/land-grants.js b/src/server/common/helpers/logging/log-codes/land-grants.js
new file mode 100644
index 000000000..e9ccd94f4
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/land-grants.js
@@ -0,0 +1,53 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const LAND_GRANTS = {
+  LAND_GRANT_APPLICATION_STARTED: {
+    level: 'info',
+    messageFunc: (messageOptions) => `Land grant application started for user=${messageOptions.userId}`
+  },
+  LAND_GRANT_APPLICATION_SUBMITTED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Land grant application submitted for user=${messageOptions.userId}, referenceNumber=${messageOptions.referenceNumber}`
+  },
+  LAND_GRANT_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Land grant processing error for user=${messageOptions.userId}: ${messageOptions.errorMessage}`
+  },
+  NO_LAND_PARCELS_FOUND: {
+    level: 'warn',
+    messageFunc: (messageOptions) => `No land parcels found for sbi=${messageOptions.sbi}`
+  },
+  NO_ACTIONS_FOUND: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `No actions found | parcelId: ${messageOptions.parcelId} | sheetId: ${messageOptions.sheetId}`
+  },
+  VALIDATE_APPLICATION_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Error validating application: ${messageOptions.errorMessage} | parcelId: ${messageOptions.parcelId} | sheetId: ${messageOptions.sheetId}`
+  },
+  FETCH_ACTIONS_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Error fetching actions: ${messageOptions.errorMessage} | sbi: ${messageOptions.sbi} | parcelId: ${messageOptions.parcelId} | sheetId: ${messageOptions.sheetId}`
+  },
+  FARM_DETAILS_MISSING_FIELDS: {
+    level: 'warn',
+    messageFunc: (messageOptions) =>
+      `Missing farm contact details for sbi: ${messageOptions.sbi} | fields: ${messageOptions.missingFields.join(', ')}`
+  },
+  UNAUTHORISED_PARCEL: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Land parcel doesn't belong to sbi=${messageOptions.sbi} | selectedLandParcel: ${messageOptions.selectedLandParcel} | landParcelsForSbi=${JSON.stringify(messageOptions.landParcelsForSbi)}`
+  },
+  API_REQUEST: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Land Grants API request | endpoint: ${messageOptions.endpoint} | url: ${messageOptions.url}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/print-application.js b/src/server/common/helpers/logging/log-codes/print-application.js
new file mode 100644
index 000000000..17726fe3b
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/print-application.js
@@ -0,0 +1,14 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const PRINT_APPLICATION = {
+  SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) => `Print application viewed for referenceNumber=${messageOptions.referenceNumber}`
+  },
+  ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Print application error for user=${messageOptions.userId}, slug=${messageOptions.slug}: ${messageOptions.errorMessage}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/resource-not-found.js b/src/server/common/helpers/logging/log-codes/resource-not-found.js
new file mode 100644
index 000000000..c72ffd842
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/resource-not-found.js
@@ -0,0 +1,15 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const RESOURCE_NOT_FOUND = {
+  FORM_NOT_FOUND: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Form not found: slug=${messageOptions.slug}, userId=${messageOptions.userId || 'anonymous'}, sbi=${messageOptions.sbi || 'unknown'}, reason=${messageOptions.reason || 'not_found'}, environment=${messageOptions.environment || 'unknown'}, referer=${messageOptions.referer || 'none'}`
+  },
+  PAGE_NOT_FOUND: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Page not found: path=${messageOptions.path}, userId=${messageOptions.userId || 'anonymous'}, sbi=${messageOptions.sbi || 'unknown'}, referer=${messageOptions.referer || 'none'}, userAgent=${messageOptions.userAgent || 'unknown'}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/submission.js b/src/server/common/helpers/logging/log-codes/submission.js
new file mode 100644
index 000000000..461a389c3
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/submission.js
@@ -0,0 +1,53 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const SUBMISSION = {
+  SUBMISSION_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Grant submission successful for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}`
+  },
+  SUBMISSION_COMPLETED: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Form submission completed for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}, fields=${messageOptions.numberOfFields || 0}, status=${messageOptions.status}`
+  },
+  SUBMISSION_FAILURE: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Grant submission failed for grantType=${messageOptions.grantType}, userCrn=${messageOptions.userCrn}, userSbi=${messageOptions.userSbi}, error=${messageOptions.errorMessage}`
+  },
+  SUBMISSION_VALIDATION_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Submission validation error for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}, validationId=${messageOptions.validationId}`
+  },
+  SUBMISSION_PAYLOAD_LOG: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `Submission payload for grantType=${messageOptions.grantType}:\n${JSON.stringify(messageOptions.payload, null, 2)}`
+  },
+  SUBMISSION_REDIRECT_FAILURE: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Submission redirect failure for grantType=${messageOptions.grantType}, referenceNumber=${messageOptions.referenceNumber}. Error: ${messageOptions.errorMessage}`
+  },
+  VALIDATOR_NOT_FOUND: {
+    level: 'error',
+    messageFunc: (messageOptions) => `No validator found for grantType=${messageOptions.grantType}`
+  },
+  APPLICATION_STATUS_UPDATED: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `${messageOptions.controller}: Application status updated to ${messageOptions.status}`
+  },
+  SUBMISSION_PROCESSING: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `${messageOptions.controller}: Processing form submission, path=${messageOptions.path}`
+  },
+  SUBMISSION_REDIRECT: {
+    level: 'debug',
+    messageFunc: (messageOptions) => `${messageOptions.controller}: Redirecting to ${messageOptions.redirectPath}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/system.js b/src/server/common/helpers/logging/log-codes/system.js
new file mode 100644
index 000000000..e32c837ba
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/system.js
@@ -0,0 +1,167 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const SYSTEM = {
+  GENERIC_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) => `An error occurred: ${messageOptions.errorMessage}`
+  },
+  VIEW_DEBUG: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `View path debug: currentFile=${messageOptions.currentFilePath}, isBuilt=${messageOptions.isRunningBuiltCode}, basePath=${messageOptions.basePath}, workingDir=${messageOptions.processWorkingDir}, pathsResolved=${messageOptions.resolvedViewPaths?.length || 0}`
+  },
+  VIEW_PATH_CHECK: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `View path ${messageOptions.index}: path=${messageOptions.path}, exists=${messageOptions.exists}, isAbsolute=${messageOptions.isAbsolute}`
+  },
+  ENV_CONFIG_DEBUG: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `Environment configuration: ${messageOptions.configType} - ${JSON.stringify(messageOptions.configValues)}`
+  },
+  SERVER_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) => {
+      const suffix =
+        messageOptions.upstreamStatus !== undefined && messageOptions.upstreamStatus !== null
+          ? ` | upstreamStatus=${messageOptions.upstreamStatus}`
+          : ''
+      return `Server error occurred: ${messageOptions.errorMessage}${suffix}`
+    }
+  },
+  STARTUP_PHASE: {
+    level: 'info',
+    messageFunc: (messageOptions) => `Startup phase: ${messageOptions.phase} - ${messageOptions.status}`
+  },
+  PLUGIN_REGISTRATION: {
+    level: 'debug',
+    messageFunc: (messageOptions) => `Plugin registration: ${messageOptions.pluginName} - ${messageOptions.status}`
+  },
+  SYSTEM_STARTUP: {
+    level: 'info',
+    messageFunc: (messageOptions) => `System startup completed on port=${messageOptions.port}`
+  },
+  SYSTEM_SHUTDOWN: {
+    level: 'info',
+    messageFunc: () => 'System shutdown initiated'
+  },
+  EXTERNAL_API_CALL: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `External API call to ${messageOptions.endpoint} for user=${messageOptions.userId || 'unknown'}`
+  },
+  EXTERNAL_API_CALL_DEBUG: {
+    level: 'debug',
+    messageFunc: (messageOptions) =>
+      `External ${messageOptions.method} to ${new URL(messageOptions.endpoint).pathname} (${messageOptions.identity || 'unknown'})`
+  },
+  EXTERNAL_API_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) => {
+      const parts = [`External API error for ${messageOptions.endpoint}`]
+      if (messageOptions.service) {
+        parts.push(`service=${messageOptions.service}`)
+      }
+      if (messageOptions.upstreamStatus !== undefined && messageOptions.upstreamStatus !== null) {
+        parts.push(`upstreamStatus=${messageOptions.upstreamStatus}`)
+      }
+      if (messageOptions.attempts !== undefined && messageOptions.attempts !== null) {
+        parts.push(`attempts=${messageOptions.attempts}`)
+      }
+      return `${parts.join(' | ')}: ${messageOptions.errorMessage}`
+    }
+  },
+  GAS_ACTION_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Error invoking GAS action ${messageOptions.action} for grant ${messageOptions.grantCode}: ${messageOptions.errorMessage}`
+  },
+  BACKEND_AUTH_CONFIG_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Backend auth configuration invalid | missingKeys=${messageOptions.missingKeys?.join(', ') || 'unknown'}`
+  },
+  RELATIONSHIP_PARSE_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `extractFarmDetails: Invalid relationship format | relationships="${messageOptions.relationships}" | reason=${messageOptions.reason}`
+  },
+  CONFIG_MISSING: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Missing required configuration: ${messageOptions?.missing?.join(', ') || 'unknown'}`
+  },
+  CONFIG_INVALID: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Invalid configuration, key "${messageOptions.key}" is missing or invalid: ${messageOptions.value}`
+  },
+  WHITELIST_CONFIG_INCOMPLETE: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Incomplete whitelist configuration in form "${messageOptions.formName}" | present=${messageOptions.presentVar} | missing=${messageOptions.missingVar}`
+  },
+  CRN_ENV_VAR_MISSING: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `CRN whitelist environment variable "${messageOptions.envVar}" missing for form "${messageOptions.formName}"`
+  },
+  SBI_ENV_VAR_MISSING: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `SBI whitelist environment variable "${messageOptions.envVar}" missing for form "${messageOptions.formName}"`
+  },
+  INVALID_REDIRECT_RULES: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Invalid redirect rules in form "${messageOptions.formName}" | reason=${messageOptions.reason}`
+  },
+  CONSOLIDATED_VIEW_API_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) => {
+      const base = `Unexpected error fetching business data from Consolidated View API | sbi=${messageOptions.sbi || 'unknown'} | status=${messageOptions.statusCode || 'unknown'} | error=${messageOptions.errorMessage}`
+      return messageOptions.responseBody ? `${base} | responseBody=${messageOptions.responseBody}` : base
+    }
+  },
+  CONSOLIDATED_VIEW_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) => `Consolidated View API request successful | sbi=${messageOptions.sbi || 'unknown'}`
+  },
+  CONSOLIDATED_VIEW_PARTIAL_SUCCESS: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Partial success from Consolidated View API | sbi=${messageOptions.sbi || 'unknown'} | failedPaths=${messageOptions.failedPaths} | status=${messageOptions.statusCode || 'unknown'}`
+  },
+  CONSOLIDATED_VIEW_ADDRESS_FORMAT: {
+    level: 'info',
+    messageFunc: (messageOptions) =>
+      `Address format for sbi=${messageOptions.sbi} is ${messageOptions.uprn ? 'structured' : 'unstructured'}, uprn=${messageOptions.uprn || 'not set'}`
+  },
+  SESSION_STATE_CLEAR_FAILED: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Failed to clear application state for slug=${messageOptions.slug}, sessionKey=${messageOptions.sessionKey}, error=${messageOptions.errorMessage}`
+  },
+  SESSION_STATE_KEY_PARSE_FAILED: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Failed to parse session key: error=${messageOptions.errorMessage}, path=${messageOptions.requestPath}`
+  },
+  SESSION_STATE_FETCH_FAILED: {
+    level: 'error',
+    messageFunc: (messageOptions) =>
+      `Failed to fetch saved state: sessionKey=${messageOptions.sessionKey}, error=${messageOptions.errorMessage}, path=${messageOptions.requestPath}`
+  },
+  RATE_LIMIT_EXCEEDED: {
+    level: 'warn',
+    messageFunc: (messageOptions) =>
+      `Rate limit exceeded: path=${messageOptions.path}, ip=${messageOptions.ip || 'unknown'}, userId=${messageOptions.userId || 'anonymous'}, userAgent=${messageOptions.userAgent || 'unknown'}`
+  },
+  STATE_SIZE_EXCEEDED: {
+    level: 'warn',
+    messageFunc: (messageOptions) =>
+      `State payload size ${messageOptions.size} bytes exceeds limit of ${messageOptions.limit} bytes for sessionKey=${messageOptions.sessionKey}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log-codes/woodland.js b/src/server/common/helpers/logging/log-codes/woodland.js
new file mode 100644
index 000000000..7cb63430b
--- /dev/null
+++ b/src/server/common/helpers/logging/log-codes/woodland.js
@@ -0,0 +1,9 @@
+/**
+ * @type {Object<string, import('./definition.js').LogCodesDefinition>}
+ */
+export const WOODLAND = {
+  VALIDATE_ERROR: {
+    level: 'error',
+    messageFunc: (messageOptions) => `Woodland validation error: ${messageOptions.errorMessage}`
+  }
+}
diff --git a/src/server/common/helpers/logging/log.js b/src/server/common/helpers/logging/log.js
index afe075d5c..f59a15353 100644
--- a/src/server/common/helpers/logging/log.js
+++ b/src/server/common/helpers/logging/log.js
@@ -7,7 +7,7 @@ const logger = pino(loggerOptions)
 /**
  * Logs an event with the specified level and context.
  * @param {object} logCode - Logging options.
- * @param {import('./log-codes-definition.js').LogTypes.LogLevel} logCode.level - The log level.
+ * @param {import('./log-codes/definition.js').LogTypes.LogLevel} logCode.level - The log level.
  * @param {Function} logCode.messageFunc - A function that creates an interpolated message string
  * @param {object} [logCode.error] - An error object (optional)
  * @param {object} messageOptions - Values for message interpolation
@@ -22,7 +22,7 @@ const log = (logCode, messageOptions, request) => {
 /**
  * Logs an event with the specified level and context.
  * @param {object} logCode - Logging options.
- * @param {import('./log-codes-definition.js').LogTypes.LogLevel} logCode.level - The log level.
+ * @param {import('./log-codes/definition.js').LogTypes.LogLevel} logCode.level - The log level.
  * @param {Function} logCode.messageFunc - A function that creates an interpolated message string
  * @param {object} [logCode.error] - An error object (optional)
  * @param {object} messageOptions - Values for message interpolation
@@ -37,7 +37,7 @@ const debug = (logCode, messageOptions, request) => {
 
 /**
  * Returns the logger function corresponding to the given log level.
- * @param {import('./log-codes-definition.js').LogTypes.LogLevel} level - The log level.
+ * @param {import('./log-codes/definition.js').LogTypes.LogLevel} level - The log level.
  * @param {object} [request] - Hapi request object (optional)
  * @returns {(errorContext: object | undefined, message: string) => void} Logger function.
  */
diff --git a/src/server/common/services/consolidated-view/consolidated-view.service.js b/src/server/common/services/consolidated-view/consolidated-view.service.js
index acd80eed6..097e29298 100644
--- a/src/server/common/services/consolidated-view/consolidated-view.service.js
+++ b/src/server/common/services/consolidated-view/consolidated-view.service.js
@@ -2,7 +2,7 @@ import { config } from '~/src/config/config.js'
 import { getValidToken } from '~/src/server/common/helpers/entra/token-manager.js'
 import { escapeGraphQLString } from '~/src/server/common/helpers/graphql-utils.js'
 import { retry } from '~/src/server/common/helpers/retry.js'
-import { log, debug, LogCodes } from '~/src/server/common/helpers/logging/log.js'
+import { log, LogCodes } from '~/src/server/common/helpers/logging/log.js'
 import { ConsolidatedViewError } from '~/src/server/common/utils/errors/ConsolidatedViewError.js'
 import { statusCodes } from '../../constants/status-codes.js'
 
@@ -149,14 +149,7 @@ async function fetchFromConsolidatedView(request, { query, formatResponse, toler
 
     return formatResponse(responseJson)
   } catch (error) {
-    debug(
-      LogCodes.SYSTEM.CONSOLIDATED_VIEW_API_ERROR,
-      {
-        sbi,
-        errorMessage: error.message
-      },
-      request
-    )
+    logConsolidatedViewUpstreamError(request, sbi, error)
 
     if (error instanceof ConsolidatedViewError) {
       throw error
@@ -173,6 +166,18 @@ async function fetchFromConsolidatedView(request, { query, formatResponse, toler
   }
 }
 
+function logConsolidatedViewUpstreamError(request, sbi, error) {
+  log(
+    LogCodes.SYSTEM.CONSOLIDATED_VIEW_API_ERROR,
+    {
+      sbi,
+      statusCode: error.status ?? error.statusCode ?? null,
+      errorMessage: error.message
+    },
+    request
+  )
+}
+
 async function makeStubRequest({ query, sbi, crn }) {
   const stubUrl = config.get('consolidatedView.stubUrl')
 
diff --git a/src/server/common/services/consolidated-view/consolidated-view.service.test.js b/src/server/common/services/consolidated-view/consolidated-view.service.test.js
index 9283e9f6e..7e27cc4a9 100644
--- a/src/server/common/services/consolidated-view/consolidated-view.service.test.js
+++ b/src/server/common/services/consolidated-view/consolidated-view.service.test.js
@@ -10,6 +10,7 @@ import {
   fetchBusinessAndCPH
 } from './consolidated-view.service.js'
 import { retry } from '~/src/server/common/helpers/retry.js'
+import { log } from '~/src/server/common/helpers/logging/log.js'
 
 vi.mock('~/src/server/common/helpers/retry.js')
 
@@ -256,6 +257,26 @@ describe('Consolidated View Service', () => {
       )
     })
 
+    it('should log CONSOLIDATED_VIEW_API_ERROR at error level on upstream failure', async () => {
+      mockFetchInstance.mockResolvedValueOnce({
+        ok: false,
+        status: 500,
+        statusText: 'Internal Server Error',
+        text: () => Promise.resolve('Server error')
+      })
+
+      await expect(fetchBusinessAndCPH(mockRequest)).rejects.toThrow()
+
+      expect(log).toHaveBeenCalledWith(
+        expect.objectContaining({ level: 'error' }),
+        expect.objectContaining({
+          sbi: mockSbi,
+          errorMessage: expect.stringContaining('500')
+        }),
+        mockRequest
+      )
+    })
+
     it('should use stub endpoint in mock mode', async () => {
       config.set('consolidatedView', {
         apiEndpoint: 'https://api.example.com/graphql',
diff --git a/src/server/common/services/grant-application/grant-application.service.js b/src/server/common/services/grant-application/grant-application.service.js
index cb6fc0cfd..0d13c94a4 100644
--- a/src/server/common/services/grant-application/grant-application.service.js
+++ b/src/server/common/services/grant-application/grant-application.service.js
@@ -1,5 +1,5 @@
 import { config } from '~/src/config/config.js'
-import { debug } from '~/src/server/common/helpers/logging/log.js'
+import { log, LogCodes } from '~/src/server/common/helpers/logging/log.js'
 import { retry } from '~/src/server/common/helpers/retry.js'
 import { statusCodes } from '../../constants/status-codes.js'
 
@@ -100,6 +100,19 @@ async function handleResponse(response, grantCode) {
   return response
 }
 
+function logGasUpstreamError(request, url, error) {
+  log(
+    LogCodes.SYSTEM.EXTERNAL_API_ERROR,
+    {
+      endpoint: url,
+      service: 'grant-application-service',
+      upstreamStatus: error.status ?? null,
+      errorMessage: error.message
+    },
+    request
+  )
+}
+
 /**
  * Makes a request to the Grant Application Service (GAS) API
  * @param {string} url - API endpoint URL
@@ -135,15 +148,7 @@ export async function makeGasApiRequest(url, grantCode, request, options = {}) {
 
     return response
   } catch (error) {
-    debug(
-      {
-        level: 'error',
-        error,
-        messageFunc: () => 'Unexpected error in GAS API request: ' + error.message
-      },
-      {},
-      request
-    )
+    logGasUpstreamError(request, url, error)
     if (error instanceof GrantApplicationServiceApiError) {
       throw error
     }
diff --git a/src/server/common/services/grant-application/grant-application.service.test.js b/src/server/common/services/grant-application/grant-application.service.test.js
index da63610dd..4e405fcba 100644
--- a/src/server/common/services/grant-application/grant-application.service.test.js
+++ b/src/server/common/services/grant-application/grant-application.service.test.js
@@ -2,6 +2,7 @@ import { beforeEach, vi } from 'vitest'
 import { mockFetch, mockFetchWithResponse, mockSimpleRequest } from '~/src/__mocks__/hapi-mocks.js'
 import { config } from '~/src/config/config.js'
 import { retry } from '~/src/server/common/helpers/retry.js'
+import { log } from '~/src/server/common/helpers/logging/log.js'
 
 let invokeGasGetAction
 let invokeGasPostAction
@@ -249,6 +250,27 @@ describe('Grant Application service (token present)', () => {
         body: JSON.stringify(payload)
       })
     })
+
+    test('should log EXTERNAL_API_ERROR with service and upstreamStatus on GAS 5xx', async () => {
+      const mockedFetch = mockFetch()
+      mockedFetch.mockResolvedValue({
+        ok: false,
+        status: 502,
+        json: () => ({ message: 'Bad Gateway' }),
+        statusText: 'Bad Gateway'
+      })
+
+      await expect(invokeGasPostAction(code, actionName, payload)).rejects.toThrow()
+
+      expect(log).toHaveBeenCalledWith(
+        expect.objectContaining({ level: 'error' }),
+        expect.objectContaining({
+          service: 'grant-application-service',
+          upstreamStatus: 502
+        }),
+        undefined
+      )
+    })
   })
 
   describe('invokeGasGetAction', () => {
diff --git a/src/server/common/utils/errors/BaseError.js b/src/server/common/utils/errors/BaseError.js
index 0daad6d55..f8d69d294 100644
--- a/src/server/common/utils/errors/BaseError.js
+++ b/src/server/common/utils/errors/BaseError.js
@@ -1,7 +1,7 @@
 /**
  * @typedef {typeof import('../../constants/status-codes.js').statusCodes} StatusCodes
  * @typedef {(StatusCodes)[keyof StatusCodes]} StatusCode
- * @typedef {import('../../helpers/logging/log-codes-definition.js').LogCodesDefinition} LogDefinition
+ * @typedef {import('../../helpers/logging/log-codes/definition.js').LogCodesDefinition} LogDefinition
  *
  */
 
diff --git a/src/server/land-grants/services/land-grants.client.js b/src/server/land-grants/services/land-grants.client.js
index d5f27fa50..c0deca437 100644
--- a/src/server/land-grants/services/land-grants.client.js
+++ b/src/server/land-grants/services/land-grants.client.js
@@ -3,11 +3,29 @@ import { log, LogCodes } from '~/src/server/common/helpers/logging/log.js'
 import { retry } from '~/src/server/common/helpers/retry.js'
 import { getConsentTypes } from '~/src/server/land-grants/utils/consent-types.js'
 
+const LAND_GRANTS_SERVICE = 'grants-ui-backend'
+
+/**
+ * @param {string} endpoint
+ * @param {number | null | undefined} status
+ * @param {string} errorMessage
+ * @param {number} [attempts]
+ */
+function logUpstreamError(endpoint, status, errorMessage, attempts) {
+  log(LogCodes.SYSTEM.EXTERNAL_API_ERROR, {
+    endpoint,
+    service: LAND_GRANTS_SERVICE,
+    upstreamStatus: status,
+    ...(attempts === undefined ? {} : { attempts }),
+    errorMessage
+  })
+}
+
 /**
  * Performs a POST request to the Land Grants API.
  * @template T
  * @param {string} endpoint
- * @param {object} body
+ * @param {Record<string, unknown>} body
  * @param {string} baseUrl
  * @returns {Promise<T>}
  * @throws {Error}
@@ -16,7 +34,12 @@ export async function postToLandGrantsApi(endpoint, body, baseUrl) {
   const url = `${baseUrl}${endpoint}`
   log(LogCodes.LAND_GRANTS.API_REQUEST, { endpoint, url })
 
+  let attempts = 0
+  /** @type {number | null} */
+  let lastUpstreamStatus = null
+
   const apiOperation = async () => {
+    attempts += 1
     const response = await fetch(url, {
       method: 'POST',
       headers: /** @type {HeadersInit} */ (createApiHeadersForLandGrantsBackend()),
@@ -25,6 +48,8 @@ export async function postToLandGrantsApi(endpoint, body, baseUrl) {
 
     if (!response.ok) {
       await response.arrayBuffer()
+      lastUpstreamStatus = response.status
+      logUpstreamError(endpoint, response.status, response.statusText)
       /**
        * @type {Error & {code?: number, status?: number}}
        */
@@ -37,10 +62,15 @@ export async function postToLandGrantsApi(endpoint, body, baseUrl) {
     return response.json()
   }
 
-  return retry(apiOperation, {
+  const result = await retry(apiOperation, {
     timeout: 30000,
     serviceName: `LandGrantsApi.postTo ${endpoint}`
+  }).catch((error) => {
+    logUpstreamError(endpoint, error.status ?? error.code ?? lastUpstreamStatus, error.message, attempts)
+    throw error
   })
+
+  return result
 }
 
 /**
diff --git a/src/server/land-grants/services/land-grants.client.test.js b/src/server/land-grants/services/land-grants.client.test.js
index bc93db583..f50a52f02 100644
--- a/src/server/land-grants/services/land-grants.client.test.js
+++ b/src/server/land-grants/services/land-grants.client.test.js
@@ -9,21 +9,10 @@ import {
 } from './land-grants.client.js'
 import { vi } from 'vitest'
 import { retry } from '~/src/server/common/helpers/retry.js'
+import { log } from '~/src/server/common/helpers/logging/log.js'
 
 vi.mock('~/src/server/common/helpers/retry.js')
 
-vi.mock('~/src/server/common/helpers/logging/log.js', () => ({
-  log: vi.fn(),
-  LogCodes: {
-    LAND_GRANTS: {
-      API_REQUEST: {
-        level: 'info',
-        messageFunc: (opts) => `Land Grants API request | endpoint: ${opts.endpoint} | url: ${opts.url}`
-      }
-    }
-  }
-}))
-
 /** @type {import('vitest').MockedFunction<any>} */
 const mockFetch = vi.fn()
 
@@ -224,10 +213,9 @@ describe('Land Grants client', () => {
       )
     })
 
-    it('should handle error with different status codes', async () => {
-      const statusCodes = [400, 401, 403, 500, 502, 503]
-
-      for (const status of statusCodes) {
+    it.each([400, 401, 403, 500, 502, 503])(
+      'propagates upstream status %i as both error.code and error.status',
+      async (status) => {
         mockFetch.mockResolvedValueOnce({
           ok: false,
           status,
@@ -235,14 +223,140 @@ describe('Land Grants client', () => {
           arrayBuffer: vi.fn().mockResolvedValue(undefined)
         })
 
-        try {
-          await postToLandGrantsApi('/test', {}, mockApiEndpoint)
-          expect.fail('Should have thrown an error')
-        } catch (error) {
-          expect(error.status).toBe(status)
-          expect(error.code).toBe(status)
-        }
+        await expect(postToLandGrantsApi('/test', {}, mockApiEndpoint)).rejects.toMatchObject({
+          code: status,
+          status
+        })
       }
+    )
+
+    it('should log EXTERNAL_API_ERROR with upstreamStatus and service when BE returns 502', async () => {
+      mockFetch.mockResolvedValueOnce({
+        ok: false,
+        status: 502,
+        statusText: 'Bad Gateway',
+        arrayBuffer: vi.fn().mockResolvedValue(undefined)
+      })
+
+      await expect(postToLandGrantsApi('/test', {}, mockApiEndpoint)).rejects.toThrow('Bad Gateway')
+
+      // Call-site log: fired before the error is rethrown, capturing upstream status
+      expect(log).toHaveBeenCalledWith(
+        expect.objectContaining({ level: 'error' }),
+        expect.objectContaining({
+          endpoint: '/test',
+          service: 'grants-ui-backend',
+          upstreamStatus: 502,
+          errorMessage: 'Bad Gateway'
+        })
+      )
+    })
+
+    it('should log EXTERNAL_API_ERROR with attempts after retry exhaustion', async () => {
+      // Make retry behave as if it tried multiple times before giving up.
+      retry.mockImplementationOnce(async (operation) => {
+        await operation().catch(() => {})
+        await operation().catch(() => {})
+        return operation()
+      })
+      mockFetch.mockResolvedValue({
+        ok: false,
+        status: 502,
+        statusText: 'Bad Gateway',
+        arrayBuffer: vi.fn().mockResolvedValue(undefined)
+      })
+
+      await expect(postToLandGrantsApi('/test', {}, mockApiEndpoint)).rejects.toThrow('Bad Gateway')
+
+      const exhaustionLogCall = log.mock.calls.find(
+        ([code, opts]) => code?.level === 'error' && opts?.attempts !== undefined
+      )
+      expect(exhaustionLogCall).toBeDefined()
+      expect(exhaustionLogCall[1]).toEqual(
+        expect.objectContaining({
+          endpoint: '/test',
+          service: 'grants-ui-backend',
+          upstreamStatus: 502,
+          attempts: 3,
+          errorMessage: 'Bad Gateway'
+        })
+      )
+    })
+
+    it('should fall back to lastUpstreamStatus when retry error has no status or code', async () => {
+      // Simulate a retry-level failure (e.g. timeout) where the rejected error has no status/code,
+      // but the inner operation already captured an upstream status via lastUpstreamStatus.
+      retry.mockImplementationOnce(async (operation) => {
+        await operation().catch(() => {})
+        const timeoutError = new Error('Operation timed out')
+        throw timeoutError
+      })
+      mockFetch.mockResolvedValueOnce({
+        ok: false,
+        status: 502,
+        statusText: 'Bad Gateway',
+        arrayBuffer: vi.fn().mockResolvedValue(undefined)
+      })
+
+      await expect(postToLandGrantsApi('/test', {}, mockApiEndpoint)).rejects.toThrow('Operation timed out')
+
+      const exhaustionLogCall = log.mock.calls.find(
+        ([code, opts]) => code?.level === 'error' && opts?.errorMessage === 'Operation timed out'
+      )
+      expect(exhaustionLogCall).toBeDefined()
+      expect(exhaustionLogCall[1]).toEqual(
+        expect.objectContaining({
+          endpoint: '/test',
+          service: 'grants-ui-backend',
+          upstreamStatus: 502,
+          errorMessage: 'Operation timed out'
+        })
+      )
+    })
+
+    it('should pass null upstreamStatus when no upstream response was received', async () => {
+      // Network-level failure: fetch rejects before any HTTP response arrives.
+      retry.mockImplementationOnce(async () => {
+        throw new Error('Network down')
+      })
+
+      await expect(postToLandGrantsApi('/test', {}, mockApiEndpoint)).rejects.toThrow('Network down')
+
+      const exhaustionLogCall = log.mock.calls.find(
+        ([code, opts]) => code?.level === 'error' && opts?.errorMessage === 'Network down'
+      )
+      expect(exhaustionLogCall).toBeDefined()
+      expect(exhaustionLogCall[1]).toEqual(
+        expect.objectContaining({
+          endpoint: '/test',
+          service: 'grants-ui-backend',
+          upstreamStatus: null,
+          errorMessage: 'Network down'
+        })
+      )
+    })
+
+    it('should use error.code when error.status is missing', async () => {
+      retry.mockImplementationOnce(async () => {
+        const err = /** @type {Error & {code?: number}} */ (new Error('Forbidden'))
+        err.code = 403
+        throw err
+      })
+
+      await expect(postToLandGrantsApi('/test', {}, mockApiEndpoint)).rejects.toThrow('Forbidden')
+
+      const exhaustionLogCall = log.mock.calls.find(
+        ([code, opts]) => code?.level === 'error' && opts?.errorMessage === 'Forbidden'
+      )
+      expect(exhaustionLogCall).toBeDefined()
+      expect(exhaustionLogCall[1]).toEqual(
+        expect.objectContaining({
+          endpoint: '/test',
+          service: 'grants-ui-backend',
+          upstreamStatus: 403,
+          errorMessage: 'Forbidden'
+        })
+      )
     })
 
     it('should return the exact response from json()', async () => {
diff --git a/types/hapi-augmentations.d.ts b/types/hapi-augmentations.d.ts
index 0c4b238d6..4fca2c669 100644
--- a/types/hapi-augmentations.d.ts
+++ b/types/hapi-augmentations.d.ts
@@ -4,4 +4,14 @@ declare module '@hapi/hapi' {
   interface ServerMethods {
     getFormService: () => object
   }
+
+  // Mirrors @defra/forms-engine-plugin's augmentation, which our tsc can't
+  // resolve because the plugin's .d.ts uses path aliases (~/src/...).
+  interface RequestApplicationState {
+    model?: {
+      def?: {
+        metadata?: Record<string, unknown>
+      }
+    }
+  }
 }