diff --git a/.husky/pre-commit b/.husky/pre-commit
index 251a23e7..6f5cf54d 100755
--- a/.husky/pre-commit
+++ b/.husky/pre-commit
@@ -1,4 +1,5 @@
 #!/usr/bin/env sh
 . "$(dirname -- "$0")/_/husky.sh"
 
-npm run lint
\ No newline at end of file
+npm run lint:fix
+npm run lint
diff --git a/src/controllers/uploadController.js b/src/controllers/uploadController.js
index fc00d304..9af2c1a5 100644
--- a/src/controllers/uploadController.js
+++ b/src/controllers/uploadController.js
@@ -18,30 +18,40 @@ class UploadController extends Controller {
   }
 
   async post (req, res, next) {
+    if (req.file !== undefined) {
+      try {
+        const jsonResult = await this.validateFile({
+          filePath: req.file.path,
+          fileName: req.file.originalname,
+          dataset: req.sessionModel.get('dataset'),
+          dataSubject: req.sessionModel.get('data-subject'),
+          organization: 'mockOrg'
+        })
+        req.body.validationResult = jsonResult
+      } catch (error) {
+        console.log(error)
+      }
+    }
+    super.post(req, res, next)
+  }
+
+  async validateFile ({ filePath, fileName, dataset, dataSubject, organization }) {
     const formData = new FormData()
-    formData.append('dataset', req.sessionModel.get('dataset'))
-    formData.append('collection', req.sessionModel.get('data-subject'))
-    formData.append('organization', 'mockOrg')
+    formData.append('dataset', dataset)
+    formData.append('collection', dataSubject)
+    formData.append('organization', organization)
 
-    const filePath = req.file.path
     const file = new Blob([await readFile(filePath)], { type: lookup(filePath) })
 
-    formData.append('upload_file', file, req.file.originalname)
+    formData.append('upload_file', file, fileName)
 
-    try {
-      // post the data to the api
-      const result = await fetch(apiRoute, {
-        method: 'POST',
-        body: formData
-      })
+    // post the data to the api
+    const result = await fetch(apiRoute, {
+      method: 'POST',
+      body: formData
+    })
 
-      const json = await result.json()
-
-      req.sessionModel.set('validationResult', json)
-      super.post(req, res, next)
-    } catch (e) {
-      res.send(e)
-    }
+    return await result.json()
   }
 }
 
diff --git a/src/routes/form-wizard/steps.js b/src/routes/form-wizard/steps.js
index 6a066ded..87a89d0f 100644
--- a/src/routes/form-wizard/steps.js
+++ b/src/routes/form-wizard/steps.js
@@ -16,6 +16,7 @@ module.exports = {
   },
   '/upload': {
     controller: require('../../controllers/uploadController'),
+    fields: ['validationResult'],
     next: 'errors'
   },
   '/errors': {
diff --git a/src/views/data-subject.html b/src/views/data-subject.html
index e762c8b8..4a26f76d 100644
--- a/src/views/data-subject.html
+++ b/src/views/data-subject.html
@@ -3,9 +3,28 @@
 {% from 'govuk/components/back-link/macro.njk' import govukBackLink %}
 {% from 'govuk/components/button/macro.njk' import govukButton %}
 {% from 'govuk/components/radios/macro.njk' import govukRadios %}
+{% from 'govuk/components/error-message/macro.njk' import govukErrorMessage %}
+{% from 'govuk/components/error-summary/macro.njk' import govukErrorSummary %}
+
+
 
 {% set pageName = 'Data subject' %}
 
+{% set errorMessage = 'Please select a data subject' %}
+
+{% if 'data-subject' in errors %}
+  {% set dataSubjectError = true %}
+{% endif %}
+
+{% block pageTitle %}
+  {% if dataSubjectError %}
+    Error: {{super()}}
+  {% else %}
+    {{super()}}
+  {% endif %}
+{% endblock %}
+
+
 {% block beforeContent %}
   {{ govukBackLink({
     text: "Back",
@@ -16,6 +35,17 @@
 {% block content %}
   <div class="govuk-grid-row">
     <div class="govuk-grid-column-two-thirds">
+      {% if dataSubjectError %}
+        {{ govukErrorSummary({
+          titleText: "There is a problem",
+          errorList: [
+            {
+              text: errorMessage,
+              href: "#data-subject"
+            }
+          ]
+        }) }}
+      {% endif %}
       <form novalidate method="post">
 
         {{ govukRadios({
@@ -46,7 +76,10 @@
               text: "Tree preservation order"
             }
           ],
-          value: data.check.dataSubject
+          value: data.check.dataSubject,
+          errorMessage: {
+            text: errorMessage 
+          } if dataSubjectError else undefined
         }) }}
 
         {{ govukButton({
diff --git a/src/views/dataset.html b/src/views/dataset.html
index f4559f87..3f3c844d 100644
--- a/src/views/dataset.html
+++ b/src/views/dataset.html
@@ -2,9 +2,26 @@
 {% from 'govuk/components/back-link/macro.njk' import govukBackLink %}
 {% from 'govuk/components/button/macro.njk' import govukButton %}
 {% from 'govuk/components/radios/macro.njk' import govukRadios %}
+{% from 'govuk/components/error-message/macro.njk' import govukErrorMessage %}
+{% from 'govuk/components/error-summary/macro.njk' import govukErrorSummary %}
 
 {% set pageName = 'Dataset' %}
 
+{% set errorMessage = 'Please select a dataset' %}
+
+
+{% if 'dataset' in errors %}
+  {% set datasetError = true %}
+{% endif %}
+
+{% block pageTitle %}
+  {% if datasetError %}
+    Error: {{super()}}
+  {% else %}
+    {{super()}}
+  {% endif %}
+{% endblock %}
+
 {% block beforeContent %}
   {{ govukBackLink({
     text: "Back",
@@ -13,28 +30,42 @@
 {% endblock %}
 
 {% block content %}
-  <div class="govuk-grid-row">
-    <div class="govuk-grid-column-two-thirds">
-      <form novalidate method="post">
-
-        {{ govukRadios({
-          idPrefix: "dataset",
-          name: "dataset",
-          fieldset: {
-            legend: {
-              text: pageName,
-              isPageHeading: true,
-              classes: "govuk-fieldset__legend--l"
-            }
-          },
-          items: options.datasetItems,
-          value: data.check.dataset
-        }) }}
-
-        {{ govukButton({
-          text: "Continue"
-        }) }}
-      </form>
-    </div>
+<div class="govuk-grid-row">
+  <div class="govuk-grid-column-two-thirds">
+    {% if datasetError %}
+      {{ govukErrorSummary({
+        titleText: "There is a problem",
+        errorList: [
+          {
+            text: errorMessage,
+            href: "#dataset"
+          }
+        ]
+      }) }}
+    {% endif %}
+    <form novalidate method="post">
+
+      {{ govukRadios({
+        idPrefix: "dataset",
+        name: "dataset",
+        fieldset: {
+          legend: {
+            text: pageName,
+            isPageHeading: true,
+            classes: "govuk-fieldset__legend--l"
+          }
+        },
+        items: options.datasetItems,
+        value: data.check.dataset,
+        errorMessage: {
+          text: errorMessage 
+        } if datasetError else undefined
+      }) }}
+
+      {{ govukButton({
+        text: "Continue"
+      }) }}
+    </form>
   </div>
+</div>
 {% endblock %}
diff --git a/src/views/pages/file-not-found.html b/src/views/pages/file-not-found.html
new file mode 100644
index 00000000..e69de29b
diff --git a/src/views/upload.html b/src/views/upload.html
index d3465eec..8e4e3031 100644
--- a/src/views/upload.html
+++ b/src/views/upload.html
@@ -3,9 +3,27 @@
 {% from "govuk/components/back-link/macro.njk" import govukBackLink %}
 {% from "govuk/components/file-upload/macro.njk" import govukFileUpload %}
 {% from "govuk/components/button/macro.njk" import govukButton %}
+{% from 'govuk/components/error-message/macro.njk' import govukErrorMessage %}
+{% from 'govuk/components/error-summary/macro.njk' import govukErrorSummary %}
+
 
 {% set pageName = 'Upload data' %}
 
+{% set errorMessage = 'Please select a file' %}
+
+
+{% if 'validationResult' in errors %}
+  {% set datasetError = true %}
+{% endif %}
+
+{% block pageTitle %}
+  {% if datasetError %}
+    Error: {{super()}}
+  {% else %}
+    {{super()}}
+  {% endif %}
+{% endblock %}
+
 {% block beforeContent %}
   {{ govukBackLink({
     text: "Back",
@@ -16,6 +34,17 @@
 {% block content %}
   <div class="govuk-grid-row">
     <div class="govuk-grid-column-two-thirds">
+      {% if datasetError %}
+        {{ govukErrorSummary({
+          titleText: "There is a problem",
+          errorList: [
+            {
+              text: errorMessage,
+              href: "#datafile"
+            }
+          ]
+        }) }}
+      {% endif %}
       <form novalidate method="post" enctype="multipart/form-data">
 
         {{ govukFileUpload({
@@ -28,7 +57,10 @@
           },
           hint: {
             text: "You can upload a CSV, GeoJSON, GML or Geopackage file"
-          }
+          },
+          errorMessage: {
+            text: errorMessage 
+          } if datasetError else undefined
         }) }}
         {{ govukButton({
           text: "Continue"
diff --git a/test/acceptance/validation_errors.test.js b/test/acceptance/validation_errors.test.js
new file mode 100644
index 00000000..c283ac5a
--- /dev/null
+++ b/test/acceptance/validation_errors.test.js
@@ -0,0 +1,82 @@
+import { test, expect } from '@playwright/test'
+
+test('when the user clicks continue on the data subject page without entering a data subject, the page correctly indicates there\'s an error', async ({ page }) => {
+  await page.goto('/')
+  await page.getByRole('button', { name: 'Start now' }).click()
+  await page.getByRole('button', { name: 'Continue' }).click()
+
+  await page.waitForSelector('input#data-subject.govuk-radios__input')
+
+  const errorLink = await page.getByRole('link', { name: 'Please select a data subject' })
+  const fieldError = await page.getByText('Error: Please select a data subject')
+  const errorSummary = await page.getByText('There is a problem')
+
+  expect(await errorSummary.isVisible(), 'Page should show the error summary').toBeTruthy()
+  expect(await errorLink.isVisible(), 'Page should the error message that is a link to the problem field').toBeTruthy()
+  expect(await fieldError.isVisible(), 'Page should show the error message next to the problem field').toBeTruthy()
+  await errorLink.click()
+  const problemFieldIsFocused = await page.$eval('input#data-subject.govuk-radios__input', (el) => el === document.activeElement)
+  expect(problemFieldIsFocused, 'The focus should be on the problem field').toBeTruthy()
+
+  expect(await page.title(), 'Page title should indicate there\'s an error').toMatch(/Error: .*/)
+})
+
+test('when the user clicks continue on the dataset page without entering a dataset, the page correctly indicates there\'s an error', async ({ page }) => {
+  await page.goto('/')
+  // start page
+  await page.getByRole('button', { name: 'Start now' }).click()
+
+  // data subject page
+  await page.getByLabel('Conservation area').check()
+  await page.getByRole('button', { name: 'Continue' }).click()
+
+  // dataset page
+  await page.getByRole('button', { name: 'Continue' }).click()
+
+  await page.waitForSelector('input#dataset.govuk-radios__input')
+
+  const errorLink = await page.getByRole('link', { name: 'Please select a dataset' })
+  const fieldError = await page.getByText('Error: Please select a dataset')
+  const errorSummary = await page.getByText('There is a problem')
+
+  expect(await errorSummary.isVisible(), 'Page should show the error summary').toBeTruthy()
+  expect(await errorLink.isVisible(), 'Page should the error message that is a link to the problem field').toBeTruthy()
+  expect(await fieldError.isVisible(), 'Page should show the error message next to the problem field').toBeTruthy()
+  await errorLink.click()
+  const problemFieldIsFocused = await page.$eval('input#dataset.govuk-radios__input', (el) => el === document.activeElement)
+  expect(problemFieldIsFocused, 'The focus should be on the problem field').toBeTruthy()
+
+  expect(await page.title(), 'Page title should indicate there\'s an error').toMatch(/Error: .*/)
+})
+
+test('when the user clicks continue on the file upload page without selecting a file, the page correctly indicates there\'s an error', async ({ page }) => {
+  await page.goto('/')
+  // start page
+  await page.getByRole('button', { name: 'Start now' }).click()
+
+  // data subject page
+  await page.getByLabel('Conservation area').check()
+  await page.getByRole('button', { name: 'Continue' }).click()
+
+  // dataset page
+  await page.getByLabel('Conservation area dataset').check()
+  await page.getByRole('button', { name: 'Continue' }).click()
+
+  // file upload page
+  await page.getByRole('button', { name: 'Continue' }).click()
+  await page.waitForSelector('input#datafile.govuk-file-upload')
+
+  const errorLink = await page.getByRole('link', { name: 'Please select a file' })
+  const fieldError = await page.getByText('Error: Please select a file')
+  const errorSummary = await page.getByText('There is a problem')
+
+  expect(await errorSummary.isVisible(), 'Page should show the error summary').toBeTruthy()
+  expect(await errorLink.isVisible(), 'Page should the error message that is a link to the problem field').toBeTruthy()
+  expect(await fieldError.isVisible(), 'Page should show the error message next to the problem field').toBeTruthy()
+  await errorLink.click()
+
+  const problemFieldIsFocused = await page.$eval('input#datafile.govuk-file-upload', (el) => el === document.activeElement)
+  expect(problemFieldIsFocused, 'The focus should be on the problem field').toBeTruthy()
+
+  expect(await page.title(), 'Page title should indicate there\'s an error').toMatch(/Error: .*/)
+})
diff --git a/test/unit/uploadController.test.js b/test/unit/uploadController.test.js
index 9222a783..9aef7d6d 100644
--- a/test/unit/uploadController.test.js
+++ b/test/unit/uploadController.test.js
@@ -24,7 +24,8 @@ describe('UploadController', () => {
       sessionModel: {
         get: () => 'test',
         set: vi.fn()
-      }
+      },
+      body: {}
     }
     const res = {
       send: vi.fn(),
@@ -34,6 +35,6 @@ describe('UploadController', () => {
 
     await uploadController.post(req, res, next)
 
-    expect(req.sessionModel.set).toHaveBeenCalledWith('validationResult', mockApiValue)
+    expect(req.body.validationResult).toEqual(mockApiValue)
   })
 })