diff --git a/CHANGELOG.md b/CHANGELOG.md
index a2268e269c..eebdfb8e06 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,28 @@ For advice on how to use these release notes see [our guidance on staying up to
 
 ### New features
 
+#### We've updated the list of organisations and brand colours included in Frontend
+
+We've overhauled the list of organisations and organisation brand colours that are shipped with GOV.UK Frontend.
+
+The previous list was outdated and had not kept up with changes to the machinery of government. We have updated the list to:
+
+- add all current government departments and their brand colours
+- add variants of brand colours that meet a 4.5:1 contrast ratio against white, where required
+- provide warnings if defunct organisations are still being referenced in your Sass code
+
+To enable these changes, set the feature flag variable `$govuk-new-organisation-colours` to `true` before you import GOV.UK Frontend in your Sass files:
+
+```scss
+// application.scss
+$govuk-new-organisation-colours: true;
+@import "govuk-frontend/all";
+```
+
+You can also silence warnings about defunct organisations by adding `organisation-colours` to the [`$govuk-suppressed-warnings`](https://frontend.design-system.service.gov.uk/sass-api-reference/#govuk-suppressed-warnings) setting.
+
+This change was introduced in [pull request #3407: Update organisation colours](https://github.com/alphagov/govuk-frontend/pull/3407).
+
 #### Stop long words breaking out of components with `govuk-!-text-break-word`
 
 We've added a new override class to help display long or unpredictable words on narrow screens, such as an email address entered by a user.
@@ -20,6 +42,18 @@ Sass users can also use the `govuk-text-break-word` mixin.
 
 This change was introduced in [pull request #5159: Add break-word typography helper](https://github.com/alphagov/govuk-frontend/pull/5159).
 
+### Recommended changes
+
+#### Update the `$websafe` parameter on the `govuk-organisation-colour` function
+
+The `govuk-organisation-colour` Sass function's `$websafe` parameter on has been renamed to `$contrast-safe`.
+
+This is to more accurately describe the functionality of the parameter.
+
+The old parameter name will stop working in the next major version of GOV.UK Frontend.
+
+This change was introduced in [pull request #3407: Update organisation colours](https://github.com/alphagov/govuk-frontend/pull/3407).
+
 ### Fixes
 
 We've made fixes to GOV.UK Frontend in the following pull requests:
diff --git a/packages/govuk-frontend-review/src/stylesheets/app.scss b/packages/govuk-frontend-review/src/stylesheets/app.scss
index 55f0f644ce..b0493b2c10 100644
--- a/packages/govuk-frontend-review/src/stylesheets/app.scss
+++ b/packages/govuk-frontend-review/src/stylesheets/app.scss
@@ -1,8 +1,12 @@
 $govuk-show-breakpoints: true;
 $govuk-new-typography-scale: true;
+$govuk-new-organisation-colours: true;
+
+$govuk-suppressed-warnings: ("organisation-colours");
 
 @import "govuk/all";
 @import "partials/app";
 @import "partials/code";
 @import "partials/banner";
+@import "partials/organisation-swatch";
 @import "partials/prose";
diff --git a/packages/govuk-frontend-review/src/stylesheets/partials/_organisation-swatch.scss b/packages/govuk-frontend-review/src/stylesheets/partials/_organisation-swatch.scss
new file mode 100644
index 0000000000..8bcbdb0cda
--- /dev/null
+++ b/packages/govuk-frontend-review/src/stylesheets/partials/_organisation-swatch.scss
@@ -0,0 +1,18 @@
+.app-organisation-swatch {
+  padding-left: govuk-spacing(3);
+  border-left: 6px solid #777777;
+
+  h2 {
+    color: #777777;
+  }
+}
+
+@each $key, $map in $govuk-colours-organisations {
+  .app-organisation-swatch--#{$key} {
+    border-left-color: govuk-organisation-colour($key, $contrast-safe: false);
+
+    h2 {
+      color: govuk-organisation-colour($key);
+    }
+  }
+}
diff --git a/packages/govuk-frontend-review/src/views/examples/organisation-colours/index.njk b/packages/govuk-frontend-review/src/views/examples/organisation-colours/index.njk
new file mode 100644
index 0000000000..530467d362
--- /dev/null
+++ b/packages/govuk-frontend-review/src/views/examples/organisation-colours/index.njk
@@ -0,0 +1,210 @@
+{% from "govuk/components/back-link/macro.njk" import govukBackLink %}
+
+{% extends "layouts/examples.njk" %}
+
+{% block beforeContent %}
+  {{ govukBackLink({
+    href: "/"
+  }) }}
+{% endblock %}
+
+{% set organisations = {
+  "attorney-generals-office": {
+    "name": "Attorney General's Office",
+    "start": 1315
+  },
+  "cabinet-office": {
+    "name": "Cabinet Office",
+    "start": 1916
+  },
+  "civil-service": {
+    "name": "Civil Service"
+  },
+  "department-for-business-trade": {
+    "name": "Department for Business and Trade",
+    "start": 2023
+  },
+  "department-for-business-energy-industrial-strategy": {
+    "name": "Department for Business, Energy and Industrial Strategy",
+    "start": 2016,
+    "end": 2023
+  },
+  "department-for-business-innovation-skills": {
+    "name": "Department for Business, Innovation and Skills",
+    "start": 2009,
+    "end": 2016
+  },
+  "department-for-communities-local-government": {
+    "name": "Department for Communities and Local Government",
+    "start": 2006,
+    "end": 2018
+  },
+  "department-for-culture-media-sport": {
+    "name": "Department for Culture, Media and Sport",
+    "start": 1997
+  },
+  "department-for-digital-culture-media-sport": {
+    "name": "Department for Digital, Culture, Media and Sport",
+    "start": 2017,
+    "end": 2023
+  },
+  "department-for-education": {
+    "name": "Department for Education",
+    "start": 2010
+  },
+  "department-for-energy-security-net-zero": {
+    "name": "Department for Energy Security and Net Zero",
+    "start": 2023
+  },
+  "department-for-environment-food-rural-affairs": {
+    "name": "Department for Environment, Food and Rural Affairs",
+    "start": 2001
+  },
+  "department-for-exiting-the-european-union": {
+    "name": "Department for Exiting the European Union",
+    "start": 2016,
+    "end": 2020
+  },
+  "department-for-international-development": {
+    "name": "Department for International Development",
+    "start": 1997,
+    "end": 2020
+  },
+  "department-for-international-trade": {
+    "name": "Department for International Trade",
+    "start": 2016,
+    "end": 2023
+  },
+  "department-for-levelling-up-housing-communities": {
+    "name": "Department for Levelling Up, Housing and Communities",
+    "start": 2021,
+    "end": 2024
+  },
+  "department-for-science-innovation-technology": {
+    "name": "Department for Science, Innovation and Technology",
+    "start": 2023
+  },
+  "department-for-transport": {
+    "name": "Department for Transport",
+    "start": 2002
+  },
+  "department-for-work-pensions": {
+    "name": "Department for Work and Pensions",
+    "start": 2001
+  },
+  "department-of-energy-climate-change": {
+    "name": "Department of Energy and Climate Change",
+    "start": 2008,
+    "end": 2016
+  },
+  "department-of-health": {
+    "name": "Department of Health",
+    "start": 1988,
+    "end": 2018
+  },
+  "department-of-health-social-care": {
+    "name": "Department of Health and Social Care",
+    "start": 2018
+  },
+  "foreign-commonwealth-office": {
+    "name": "Foreign and Commonwealth Office",
+    "start": 1968,
+    "end": 2020
+  },
+  "foreign-commonwealth-development-office": {
+    "name": "Foreign, Commonwealth and Development Office",
+    "start": 2020
+  },
+  "hm-government": {
+    "name": "HM Government",
+    "start": 1707
+  },
+  "hm-revenue-customs": {
+    "name": "HM Revenue and Customs",
+    "start": 2005
+  },
+  "hm-treasury": {
+    "name": "HM Treasury"
+  },
+  "home-office": {
+    "name": "Home Office",
+    "start": 1782
+  },
+  "ministry-of-defence": {
+    "name": "Ministry of Defence",
+    "start": 1964
+  },
+  "ministry-of-housing-communities-local-government": {
+    "name": "Ministry of Housing, Communities and Local Government",
+    "start": 2018
+  },
+  "ministry-of-justice": {
+    "name": "Ministry of Justice",
+    "start": 2007
+  },
+  "northern-ireland-office": {
+    "name": "Northern Ireland Office",
+    "start": 1972
+  },
+  "office-of-the-advocate-general-for-scotland": {
+    "name": "Office of the Advocate General for Scotland",
+    "start": 1999
+  },
+  "office-of-the-leader-of-the-house-of-commons": {
+    "name": "Office of the Leader of the House of Commons",
+    "start": 1721
+  },
+  "office-of-the-leader-of-the-house-of-lords": {
+    "name": "Office of the Leader of the House of Lords",
+    "start": 1721
+  },
+  "office-of-the-secretary-of-state-for-scotland": {
+    "name": "Office of the Secretary of State for Scotland",
+    "start": 2018
+  },
+  "office-of-the-secretary-of-state-for-wales": {
+    "name": "Office of the Secretary of State for Wales",
+    "start": 2018
+  },
+  "prime-ministers-office-10-downing-street": {
+    "name": "Prime Minister's Office, 10 Downing Street",
+    "start": 2022
+  },
+  "scotland-office": {
+    "name": "Scotland Office",
+    "start": 1999,
+    "end": 2018
+  },
+  "uk-export-finance": {
+    "name": "UK Export Finance",
+    "start": 1919
+  },
+  "uk-trade-investment": {
+    "name": "UK Trade and Investment",
+    "start": 2003,
+    "end": 2016
+  },
+  "wales-office": {
+    "name": "Wales Office",
+    "start": 1999,
+    "end": 2018
+  }
+} %}
+
+{% block content %}
+  <div class="govuk-grid-row">
+    <div class="govuk-grid-column-two-thirds">
+      <h1 class="govuk-heading-xl">
+        Organisation colours
+      </h1>
+      <p class="govuk-body">Only includes organisations and departments that existed from 2010 onwards.</p>
+
+      {%- for key, data in organisations %}
+        <div class="app-organisation-swatch app-organisation-swatch--{{ key }}">
+          <h2 class="govuk-heading-s">{{ data.name }}</h2>
+          <p class="govuk-body">{{ data.start | default("????") }}&ndash;{{ data.end }}</p>
+        </div>
+      {%- endfor %}
+    </div>
+  </div>
+{% endblock %}
diff --git a/packages/govuk-frontend/src/govuk/helpers/_colour.scss b/packages/govuk-frontend/src/govuk/helpers/_colour.scss
index 5672b84b29..fc17e9fa9b 100644
--- a/packages/govuk-frontend/src/govuk/helpers/_colour.scss
+++ b/packages/govuk-frontend/src/govuk/helpers/_colour.scss
@@ -42,25 +42,61 @@
 /// Get the colour for a government organisation
 ///
 /// @param {String} $organisation - Organisation name, lowercase, hyphenated
-/// @param {Boolean} $websafe [true] - By default a 'websafe' version of the
-///   colour will be returned which meets contrast requirements . If you want to
-///   use the non-websafe version you can set this to `false` but your should
-///   ensure that you still meets contrast requirements for accessibility - for
-///   example, do not use the non-websafe version for text.
+/// @param {Boolean} $websafe - Deprecated. Use $contrast-safe instead.
+/// @param {Boolean} $contrast-safe [true] - By default a version of the colour
+///   will be returned which has a minimum 4.5:1 contrast ratio when used with
+///   white, as per the WCAG 2.1 Level AA guidelines. If you want to use the
+///   non-contrast safe version you can set this to `false` but your should
+///   ensure that you still meets contrast requirements for accessibility -
+///   for example, do not use the non-contrast safe version for text.
 ///
 /// @return {Colour} Representation of colour for organisation
 /// @throw if `$organisation` is not a known organisation
 /// @access public
 
-@function govuk-organisation-colour($organisation, $websafe: true) {
+@function govuk-organisation-colour($organisation, $websafe: null, $contrast-safe: true) {
+  // Check if the $organisation exists in the aliases map. If so, change the
+  // value of $organisation to the aliased value.
+  @if map-has-key($_govuk_colours-organisations-aliases, $organisation) {
+    $organisation: map-get($_govuk_colours-organisations-aliases, $organisation);
+  }
+
+  // Check to see if the organisation exists
   @if not map-has-key($govuk-colours-organisations, $organisation) {
     @error "Unknown organisation `#{$organisation}`";
   }
 
+  // Output a warning if $websafe is set.
+  @if $websafe and not index($govuk-suppressed-warnings, "organisation-colour-websafe-param") {
+    @warn _warning-text("organisation-colour-websafe-param",
+      "The `$websafe` parameter of `govuk-organisation-colour` has been " +
+      "renamed to `$contrast-safe`. The old parameter name will be removed in " +
+      "the next major version."
+    );
+  }
+
   $org-colour: map-get($govuk-colours-organisations, $organisation);
 
-  @if $websafe and map-has-key($org-colour, colour-websafe) {
-    @return map-get($org-colour, colour-websafe);
+  @if map-has-key($org-colour, deprecation-message) and not index($govuk-suppressed-warnings, "organisation-colours") {
+    @warn _warning-text(
+      "organisation-colours",
+      map-get($org-colour, deprecation-message)
+    );
+  }
+
+  // If the $websafe parameter is being used (it has been explicitly set as true
+  // or false), assume the user hasn't updated to use $contrast-safe yet and map
+  // the old parameter's value onto the new parameter.
+  @if type-of($websafe) != "null" {
+    $contrast-safe: $websafe;
+  }
+
+  // Determine the contrast-safe key to use depending on whether it's the new
+  // palette or the legacy palette
+  $safe-key: if($govuk-new-organisation-colours, "contrast-safe", "colour-websafe");
+
+  @if $contrast-safe and map-has-key($org-colour, $safe-key) {
+    @return map-get($org-colour, $safe-key);
   } @else {
     @return map-get($org-colour, colour);
   }
diff --git a/packages/govuk-frontend/src/govuk/helpers/colour.unit.test.js b/packages/govuk-frontend/src/govuk/helpers/colour.unit.test.js
index a1fac2e1a1..beaefdf3ca 100644
--- a/packages/govuk-frontend/src/govuk/helpers/colour.unit.test.js
+++ b/packages/govuk-frontend/src/govuk/helpers/colour.unit.test.js
@@ -103,20 +103,25 @@ describe('@function govuk-colour', () => {
 
 describe('@function govuk-organisation-colour', () => {
   const sassBootstrap = `
+    $govuk-new-organisation-colours: true;
     $govuk-colours-organisations: (
       'floo-network-authority': (
         colour: #EC22FF,
-        colour-websafe: #9A00A8
+        contrast-safe: #9A00A8
       ),
       'broom-regulatory-control': (
         colour: #A81223
+      ),
+      'house-elf-equalities-office': (
+        colour: #786999,
+        deprecation-message: 'The House Elf Equalities Office was disbanded in 2007.'
       )
     );
 
     @import "helpers/colour";
   `
 
-  it('returns the websafe colour for a given organisation by default', async () => {
+  it('returns the contrast-safe colour for a given organisation by default', async () => {
     const sass = `
       ${sassBootstrap}
 
@@ -134,7 +139,7 @@ describe('@function govuk-organisation-colour', () => {
     })
   })
 
-  it('falls back to the default colour if a websafe colour is not explicitly defined', async () => {
+  it('falls back to the default colour if a contrast-safe colour is not explicitly defined', async () => {
     const sass = `
       ${sassBootstrap}
 
@@ -152,7 +157,25 @@ describe('@function govuk-organisation-colour', () => {
     })
   })
 
-  it('can be overridden to return the non-websafe colour', async () => {
+  it('can be overridden to return the non-contrast-safe colour ($contrast-safe parameter)', async () => {
+    const sass = `
+      ${sassBootstrap}
+
+      .foo {
+        border-color: govuk-organisation-colour('floo-network-authority', $contrast-safe: false);
+      }
+    `
+
+    await expect(compileSassString(sass, sassConfig)).resolves.toMatchObject({
+      css: outdent`
+          .foo {
+            border-color: #EC22FF;
+          }
+        `
+    })
+  })
+
+  it('can be overridden to return the non-contrast-safe colour (deprecated $websafe parameter)', async () => {
     const sass = `
       ${sassBootstrap}
 
@@ -170,6 +193,26 @@ describe('@function govuk-organisation-colour', () => {
     })
   })
 
+  it('outputs a warning if the organisation has been deprecated', async () => {
+    const sass = `
+      ${sassBootstrap}
+
+      .foo {
+        color: govuk-organisation-colour('house-elf-equalities-office');
+      }
+    `
+
+    await compileSassString(sass, sassConfig)
+
+    // Expect our mocked @warn function to have been called once with a single
+    // argument, which should be the deprecation notice
+    expect(mockWarnFunction.mock.calls[0]).toEqual(
+      expect.arrayContaining([
+        'The House Elf Equalities Office was disbanded in 2007. To silence this warning, update $govuk-suppressed-warnings with key: "organisation-colours"'
+      ])
+    )
+  })
+
   it('throws an error if a non-existent organisation is requested', async () => {
     const sass = `
       ${sassBootstrap}
@@ -183,4 +226,98 @@ describe('@function govuk-organisation-colour', () => {
       'Unknown organisation `muggle-born-registration-commission`'
     )
   })
+
+  it('aliases renamed organisation keys to the equivalent key', async () => {
+    const sass = `
+      $govuk-colours-organisations: (
+        'department-for-business-trade': (
+          colour: #e52d13
+        )
+      );
+
+      @import "helpers/colour";
+
+      .foo {
+        color: govuk-organisation-colour('department-for-business-and-trade');
+      }
+    `
+
+    await expect(compileSassString(sass, sassConfig)).resolves.toMatchObject({
+      css: outdent`
+          .foo {
+            color: #e52d13;
+          }
+        `
+    })
+  })
+
+  describe('legacy palette', () => {
+    const sassBootstrapLegacy = `
+      $govuk-colours-organisations: (
+        'floo-network-authority': (
+          colour: #EC22FF,
+          colour-websafe: #9A00A8
+        ),
+        'broom-regulatory-control': (
+          colour: #A81223
+        )
+      );
+
+      @import "helpers/colour";
+    `
+
+    it('returns the contrast-safe colour for a given organisation by default', async () => {
+      const sass = `
+        ${sassBootstrapLegacy}
+
+        .foo {
+          color: govuk-organisation-colour('floo-network-authority');
+        }
+      `
+
+      await expect(compileSassString(sass, sassConfig)).resolves.toMatchObject({
+        css: outdent`
+          .foo {
+            color: #9A00A8;
+          }
+        `
+      })
+    })
+
+    it('falls back to the default colour if a contrast-safe colour is not explicitly defined', async () => {
+      const sass = `
+        ${sassBootstrapLegacy}
+
+        .foo {
+          color: govuk-organisation-colour('broom-regulatory-control');
+        }
+      `
+
+      await expect(compileSassString(sass, sassConfig)).resolves.toMatchObject({
+        css: outdent`
+          .foo {
+            color: #A81223;
+          }
+        `
+      })
+    })
+
+    it('can be overridden to return the non-contrast-safe colour ($websafe parameter)', async () => {
+      const sass = `
+        ${sassBootstrapLegacy}
+
+        .foo {
+          border-color: govuk-organisation-colour('floo-network-authority', $websafe: false);
+        }
+      `
+
+      await expect(compileSassString(sass, sassConfig)).resolves.toMatchObject({
+        css: outdent`
+          .foo {
+            border-color: #EC22FF;
+          }
+        `
+      })
+    })
+  })
 })
diff --git a/packages/govuk-frontend/src/govuk/settings/_colours-organisations.scss b/packages/govuk-frontend/src/govuk/settings/_colours-organisations.scss
index cf3193a7bc..779f671409 100644
--- a/packages/govuk-frontend/src/govuk/settings/_colours-organisations.scss
+++ b/packages/govuk-frontend/src/govuk/settings/_colours-organisations.scss
@@ -2,19 +2,213 @@
 /// @group settings/colours
 ////
 
-/// Organisation colours
+/// Feature flag for updated organisation list and colours
+///
+/// When set to true, $govuk-colours-organisations will use the new
+/// organisation list and colour selection.
+///
+/// Should be removed in 6.0.
+///
+/// @type Boolean
+/// @access public
+
+$govuk-new-organisation-colours: false !default;
+
+/// Current organisation colours
 ///
 /// @type Map
 ///
 /// @prop $organisation.colour - Colour for the given `$organisation`
-/// @prop $organisation.colour-websafe - Websafe colour for the given
-///   `$organisation`. We use `websafe` to mean strong enough contrast against
-///   white to be used for copy and meet the AAA (large text) and AA (smaller
+/// @prop $organisation.contrast-safe - 'Contrast safe' colour for the given
+///   `$organisation`. This colour has at least a 4.5:1 contrast against
+///   white, to be used for copy and meet the AAA (large text) and AA (smaller
 ///   copy) WCAG guidelines.
+/// @prop $organisation.deprecation-message - Marks this organisation as
+///   deprecated (usually because it has ceased to exist). Value is the
+///   deprecation message output to the terminal when compiling.
 ///
-/// @access public
+/// @access private
 
-$govuk-colours-organisations: (
+$_govuk-organisation-colours: (
+  "attorney-generals-office": (
+    colour: #a91c8e
+  ),
+  "cabinet-office": (
+    colour: #0056b8
+  ),
+  "civil-service": (
+    colour: #b2292e
+  ),
+  "department-for-business-trade": (
+    colour: #e52d13,
+    contrast-safe: #e02c13
+  ),
+  "department-for-business-energy-industrial-strategy": (
+    colour: #003479,
+    deprecation-message:
+      "`department-for-business-energy-industrial-strategy` was dissolved in 2023. It was replaced by `department-for-business-trade`, `department-for-energy-security-net-zero` and `department-science-innovation-technology`."
+  ),
+  "department-for-business-innovation-skills": (
+    colour: #003479,
+    deprecation-message:
+      "`department-for-business-innovation-skills` became `department-for-business-energy-industrial-strategy` in 2016. As of 2023, it is equivalent to `department-for-business-trade` or `department-science-innovation-technology`."
+  ),
+  "department-for-communities-local-government": (
+    colour: #009999,
+    contrast-safe: #008080,
+    deprecation-message:
+      "`department-for-communities-local-government` became `ministry-of-housing-communities-local-government` in 2018."
+  ),
+  "department-for-culture-media-sport": (
+    colour: #d6006e
+  ),
+  "department-for-digital-culture-media-sport": (
+    colour: #d40072,
+    deprecation-message:
+      "`department-for-digital-culture-media-sport` became `department-for-culture-media-sport` in 2023."
+  ),
+  "department-for-education": (
+    colour: #003764
+  ),
+  "department-for-energy-security-net-zero": (
+    colour: #00a33b,
+    contrast-safe: #00852f
+  ),
+  "department-for-environment-food-rural-affairs": (
+    colour: #00af43,
+    contrast-safe: #008733
+  ),
+  "department-for-exiting-the-european-union": (
+    colour: #009fe3,
+    contrast-safe: #007db6,
+    deprecation-message: "`department-for-exiting-the-european-union` was dissolved in 2020."
+  ),
+  "department-for-international-development": (
+    colour: #002878,
+    deprecation-message:
+      "`department-for-international-development` was merged into `foreign-commonwealth-development-office` in 2020."
+  ),
+  "department-for-international-trade": (
+    colour: #cf102d,
+    deprecation-message: "`department-for-international-trade` was merged into `department-for-business-trade` in 2023."
+  ),
+  "department-for-levelling-up-housing-communities": (
+    colour: #012169,
+    deprecation-message:
+      "`department-for-levelling-up-housing-communities` was renamed to `ministry-of-housing-communities-local-government` in 2024."
+  ),
+  "department-for-science-innovation-technology": (
+    colour: #00f9f8,
+    contrast-safe: #008180
+  ),
+  "department-for-transport": (
+    colour: #006853
+  ),
+  "department-for-work-pensions": (
+    colour: #00bcb5,
+    contrast-safe: #00857e
+  ),
+  "department-of-energy-climate-change": (
+    colour: #009ddb,
+    contrast-safe: #007db3,
+    deprecation-message:
+      "`department-of-energy-climate-change` was merged into `department-for-business-energy-industrial-strategy` in 2016. As of 2023, it is equivalent to `department-for-energy-security-net-zero`."
+  ),
+  "department-of-health": (
+    colour: #00ad93,
+    contrast-safe: #008573,
+    deprecation-message: "`department-of-health` became `department-of-health-social-care` in 2018."
+  ),
+  "department-of-health-social-care": (
+    colour: #00a990,
+    contrast-safe: #008674
+  ),
+  "foreign-commonwealth-office": (
+    colour: #003e74,
+    deprecation-message: "`foreign-commonwealth-office` became `foreign-commonwealth-development-office` in 2018."
+  ),
+  "foreign-commonwealth-development-office": (
+    colour: #002269
+  ),
+  "government-equalities-office": (
+    colour: #0056b8,
+    deprecation-message: "`government-equalities-office` is deprecated. Use `cabinet-office` instead."
+  ),
+  "hm-government": (
+    colour: #266ebc
+  ),
+  "hm-revenue-customs": (
+    colour: #008476
+  ),
+  "hm-treasury": (
+    colour: #b2292e
+  ),
+  "home-office": (
+    colour: #732282
+  ),
+  "ministry-of-defence": (
+    colour: #532a45
+  ),
+  "ministry-of-housing-communities-local-government": (
+    colour: #00625e
+  ),
+  "ministry-of-justice": (
+    colour: #000000
+  ),
+  "northern-ireland-office": (
+    colour: #00205c
+  ),
+  "office-of-the-advocate-general-for-scotland": (
+    colour: #00205c
+  ),
+  "office-of-the-leader-of-the-house-of-commons": (
+    colour: #497629
+  ),
+  "office-of-the-leader-of-the-house-of-lords": (
+    colour: #9c182f
+  ),
+  "office-of-the-secretary-of-state-for-scotland": (
+    colour: #00205c
+  ),
+  "office-of-the-secretary-of-state-for-wales": (
+    colour: #a8353a
+  ),
+  "prime-ministers-office-10-downing-street": (
+    colour: #0b0c0c
+  ),
+  "scotland-office": (
+    colour: #002663,
+    deprecation-message: "`scotland-office` became `office-of-the-secretary-of-state-for-scotland` in 2018."
+  ),
+  "uk-export-finance": (
+    colour: #cf102d
+  ),
+  "uk-trade-investment": (
+    colour: #c80651,
+    deprecation-message:
+      "`uk-trade-investment` became `department-for-international-trade` in 2016. As of 2023, it is equivalent to `department-for-business-trade`."
+  ),
+  "wales-office": (
+    colour: #a33038,
+    deprecation-message: "`wales-office` became `office-of-the-secretary-of-state-for-wales` in 2018."
+  )
+);
+
+/// Legacy organisation colours
+///
+/// These are the colours included with Frontend prior to 5.3.0. They will be
+/// removed in a future major version of Frontend.
+///
+/// @type Map
+///
+/// @prop $organisation.colour - Colour for the given `$organisation`
+/// @prop $organisation.colour-websafe - Optional alternative shade of the
+///   organisation colour. Despite the name, is not guaranteed to be websafe
+///   nor provide better contrast than the base colour.
+///
+/// @access private
+
+$_govuk-legacy-organisation-colours: (
   "attorney-generals-office": (
     colour: #9f1888,
     colour-websafe: #a03a88
@@ -30,7 +224,7 @@ $govuk-colours-organisations: (
     colour: #003479,
     colour-websafe: #347da4
   ),
-  "department-for-communities-and-local-government": (
+  "department-for-communities-local-government": (
     colour: #009999,
     colour-websafe: #37836e
   ),
@@ -54,11 +248,11 @@ $govuk-colours-organisations: (
     colour: #cf102d,
     colour-websafe: #005ea5
   ),
-  "department-for-business-and-trade": (
+  "department-for-business-trade": (
     colour: #cf102d,
     colour-websafe: #005ea5
   ),
-  "department-for-levelling-up-housing-and-communities": (
+  "department-for-levelling-up-housing-communities": (
     colour: #012169
   ),
   "department-for-transport": (
@@ -143,4 +337,36 @@ $govuk-colours-organisations: (
     colour: #a33038,
     colour-websafe: #7a242a
   )
+);
+
+/// Set public organisation colours variable to one of the two maps.
+/// Users can also pass their own map to this to override it entirely.
+///
+/// @type Map
+/// @access public
+
+$govuk-colours-organisations: if(
+  $govuk-new-organisation-colours,
+  $_govuk-organisation-colours,
+  $_govuk-legacy-organisation-colours
 ) !default;
+
+/// Organisation colour aliases
+///
+/// Some organisations have been renamed within our code over time. Here we
+/// map the prior key to the new equivalent key.
+///
+/// Note: This is for internal renames only. If a department has changed name
+/// or brand colour in a machinery of government change, it should be added to
+/// $govuk-colours-organisations as a new entry with any superseded
+/// organisations marked deprecated.
+///
+/// @type Map
+///
+/// @access private
+
+$_govuk-colours-organisations-aliases: (
+  "department-for-business-and-trade": "department-for-business-trade",
+  "department-for-communities-and-local-government": "department-for-communities-local-government",
+  "department-for-levelling-up-housing-and-communities": "department-for-levelling-up-housing-communities"
+);
diff --git a/packages/govuk-frontend/src/govuk/settings/colours.unit.test.js b/packages/govuk-frontend/src/govuk/settings/colours.unit.test.js
index 5bcf9e2407..b3ae3c4979 100644
--- a/packages/govuk-frontend/src/govuk/settings/colours.unit.test.js
+++ b/packages/govuk-frontend/src/govuk/settings/colours.unit.test.js
@@ -1,7 +1,36 @@
 const { compileSassString } = require('@govuk-frontend/helpers/tests')
 
 describe('Organisation colours', () => {
-  it('should define websafe colours that meet contrast requirements', async () => {
+  it('should define contrast-safe colours that meet contrast requirements', async () => {
+    const sass = `
+      $govuk-new-organisation-colours: true;
+
+      @import "settings/colours-palette";
+      @import "settings/colours-organisations";
+      @import "settings/colours-applied";
+      @import "helpers/colour";
+
+      @import "sass-color-helpers/stylesheets/color-helpers";
+
+      $minimum-contrast: 4.5;
+
+      @each $organisation in map-keys($govuk-colours-organisations) {
+
+        $colour: govuk-organisation-colour($organisation);
+        $contrast: ch-color-contrast($govuk-body-background-colour, $colour);
+
+        @if ($contrast < $minimum-contrast) {
+          @error "Contrast ratio for #{$organisation} too low."
+          + " #{$colour} on #{$govuk-body-background-colour} has a contrast of: #{$contrast}."
+          + " Must be higher than #{$minimum-contrast} for WCAG AA support.";
+        }
+      }
+    `
+
+    await expect(compileSassString(sass)).resolves
+  })
+
+  it('should define websafe colours that meet contrast requirements (legacy colours)', async () => {
     const sass = `
       @import "settings/colours-palette";
       @import "settings/colours-organisations";