diff --git a/app/main/views/organisations.py b/app/main/views/organisations.py
index 52978bd6d..50c679d50 100644
--- a/app/main/views/organisations.py
+++ b/app/main/views/organisations.py
@@ -62,10 +62,17 @@ def add_organisation():
     form = NewOrganisationForm()
 
     if form.validate_on_submit():
-        return redirect(url_for(
-            '.organisation_settings',
-            org_id=Organisation.create_from_form(form).id,
-        ))
+        try:
+            return redirect(url_for(
+                '.organisation_settings',
+                org_id=Organisation.create_from_form(form).id,
+            ))
+        except HTTPError as e:
+            msg = 'Organisation name already exists'
+            if e.status_code == 400 and msg in e.message:
+                form.name.errors.append("This organisation name is already in use")
+            else:
+                raise e
 
     return render_template(
         'views/organisations/add-organisation.html',
diff --git a/tests/app/main/views/organisations/test_organisations.py b/tests/app/main/views/organisations/test_organisations.py
index bb8f78b38..32d35683f 100644
--- a/tests/app/main/views/organisations/test_organisations.py
+++ b/tests/app/main/views/organisations/test_organisations.py
@@ -1,5 +1,3 @@
-from unittest.mock import ANY, Mock
-
 import pytest
 from bs4 import BeautifulSoup
 from flask import url_for
@@ -102,7 +100,7 @@ def test_page_to_create_new_organisation(
         ('radio', 'organisation_type', 'other'),
         ('radio', 'crown_status', 'crown'),
         ('radio', 'crown_status', 'non-crown'),
-        ('hidden', 'csrf_token', ANY),
+        ('hidden', 'csrf_token', mocker.ANY),
     ]
 
 
@@ -194,6 +192,37 @@ def test_create_new_organisation_fails_with_incorrect_input(
     assert error_message in page.select_one('.govuk-error-message').text
 
 
+def test_create_new_organisation_fails_with_duplicate_name(
+    client_request,
+    platform_admin_user,
+    mocker,
+):
+    def _create(**_kwargs):
+        json_mock = mocker.Mock(return_value={'message': 'Organisation name already exists'})
+        resp_mock = mocker.Mock(status_code=400, json=json_mock)
+        http_error = HTTPError(response=resp_mock, message="Default message")
+        raise http_error
+
+    mocker.patch(
+        'app.organisations_client.create_organisation',
+        side_effect=_create
+    )
+
+    client_request.login(platform_admin_user)
+    page = client_request.post(
+        '.add_organisation',
+        _data={
+            'name': 'Existing org',
+            'organisation_type': 'local',
+            'crown_status': 'non-crown',
+        },
+        _expected_status=200,
+    )
+
+    error_message = 'This organisation name is already in use'
+    assert error_message in page.select_one('.govuk-error-message').text
+
+
 @pytest.mark.parametrize('organisation_type, organisation, expected_status', (
     ('nhs_gp', None, 200),
     ('central', None, 403),
@@ -1048,7 +1077,7 @@ def test_update_organisation_domains_when_domain_already_exists(
     client_request.login(user)
 
     mocker.patch('app.organisations_client.update_organisation', side_effect=HTTPError(
-        response=Mock(
+        response=mocker.Mock(
             status_code=400,
             json={'result': 'error', 'message': 'Domain already exists'}
         ),
@@ -1198,7 +1227,7 @@ def test_confirm_update_organisation_with_name_already_in_use(
     mocker.patch(
         'app.organisations_client.update_organisation_name',
         side_effect=HTTPError(
-            response=Mock(
+            response=mocker.Mock(
                 status_code=400,
                 json={'result': 'error', 'message': 'Organisation name already exists'}
             ),
diff --git a/tests/app/main/views/test_add_service.py b/tests/app/main/views/test_add_service.py
index 5c4e24e25..11ef3dc0a 100644
--- a/tests/app/main/views/test_add_service.py
+++ b/tests/app/main/views/test_add_service.py
@@ -1,5 +1,6 @@
 import pytest
 from flask import session, url_for
+from notifications_python_client.errors import HTTPError
 
 from app.utils import is_gov_user
 from tests import organisation_json
@@ -309,9 +310,20 @@ def test_add_service_fails_if_service_name_fails_validation(
 
 def test_should_return_form_errors_with_duplicate_service_name_regardless_of_case(
     client_request,
-    mock_create_duplicate_service,
     mock_get_organisation_by_domain,
+    mocker,
 ):
+    def _create(**_kwargs):
+        json_mock = mocker.Mock(return_value={'message': {'name': ["Duplicate service name"]}})
+        resp_mock = mocker.Mock(status_code=400, json=json_mock)
+        http_error = HTTPError(response=resp_mock, message="Default message")
+        raise http_error
+
+    mocker.patch(
+        'app.service_api_client.create_service',
+        side_effect=_create
+    )
+
     page = client_request.post(
         'main.add_service',
         _data={
diff --git a/tests/conftest.py b/tests/conftest.py
index 98e2a551e..ae7fb8ab3 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -587,25 +587,6 @@ def mock_create_service(mocker):
         'app.service_api_client.create_service', side_effect=_create)
 
 
-@pytest.fixture(scope='function')
-def mock_create_duplicate_service(mocker):
-    def _create(
-        service_name,
-        organisation_type,
-        message_limit,
-        restricted,
-        user_id,
-        email_from,
-    ):
-        json_mock = Mock(return_value={'message': {'name': ["Duplicate service name '{}'".format(service_name)]}})
-        resp_mock = Mock(status_code=400, json=json_mock)
-        http_error = HTTPError(response=resp_mock, message="Default message")
-        raise http_error
-
-    return mocker.patch(
-        'app.service_api_client.create_service', side_effect=_create)
-
-
 @pytest.fixture(scope='function')
 def mock_update_service(mocker):
     def _update(service_id, **kwargs):