diff --git a/app/__init__.py b/app/__init__.py
index 10c82a8a1..11e7f72c0 100644
--- a/app/__init__.py
+++ b/app/__init__.py
@@ -1,4 +1,3 @@
-import itertools
 import os
 import urllib
 from datetime import datetime, timedelta, timezone
@@ -602,8 +601,10 @@ def useful_headers_after_request(response):
 
 
 def register_errorhandlers(application):  # noqa (C901 too complex)
-    def _error_response(error_code):
-        resp = make_response(render_template("error/{0}.html".format(error_code)), error_code)
+    def _error_response(error_code, error_page_template=None):
+        if error_page_template is None:
+            error_page_template = error_code
+        resp = make_response(render_template("error/{0}.html".format(error_page_template)), error_code)
         return useful_headers_after_request(resp)
 
     @application.errorhandler(HTTPError)
@@ -627,8 +628,10 @@ def register_errorhandlers(application):  # noqa (C901 too complex)
         return _error_response(error_code)
 
     @application.errorhandler(400)
-    def handle_400(error):
-        return _error_response(400)
+    def handle_client_error(error):
+        # This is tripped if we call `abort(400)`.
+        application.logger.exception('Unhandled 400 client error')
+        return _error_response(400, error_page_template=500)
 
     @application.errorhandler(410)
     def handle_gone(error):
@@ -671,19 +674,11 @@ def register_errorhandlers(application):  # noqa (C901 too complex)
             u'csrf.invalid_token: Aborting request, user_id: {user_id}',
             extra={'user_id': session['user_id']})
 
-        resp = make_response(render_template(
-            "error/400.html",
-            message=['Something went wrong, please go back and try again.']
-        ), 400)
-        return useful_headers_after_request(resp)
+        return _error_response(400, error_page_template=500)
 
     @application.errorhandler(405)
-    def handle_405(error):
-        resp = make_response(render_template(
-            "error/400.html",
-            message=['Something went wrong, please go back and try again.']
-        ), 405)
-        return useful_headers_after_request(resp)
+    def handle_method_not_allowed(error):
+        return _error_response(405, error_page_template=500)
 
     @application.errorhandler(WerkzeugHTTPException)
     def handle_http_error(error):
diff --git a/app/main/views/uploads.py b/app/main/views/uploads.py
index 60c28c894..332b6f9aa 100644
--- a/app/main/views/uploads.py
+++ b/app/main/views/uploads.py
@@ -234,7 +234,6 @@ def uploaded_letter_preview(service_id, file_id):
 @main.route("/services/<uuid:service_id>/preview-letter-image/<uuid:file_id>")
 @user_has_permissions('send_messages')
 def view_letter_upload_as_preview(service_id, file_id):
-
     try:
         page = int(request.args.get('page'))
     except ValueError:
diff --git a/app/templates/error/400.html b/app/templates/error/400.html
deleted file mode 100644
index f874031c1..000000000
--- a/app/templates/error/400.html
+++ /dev/null
@@ -1,11 +0,0 @@
-{% extends "withoutnav_template.html" %}
-{% block per_page_title %}Bad request{% endblock %}
-{% block maincolumn_content %}
-<div class="grid-row">
-    <div class="column-two-thirds">
-      <h1 class="heading-medium">
-            {{ message|join(",")}}
-        </h1>
-    </div>
-</div>
-{% endblock %}
diff --git a/tests/app/main/test_errorhandlers.py b/tests/app/main/test_errorhandlers.py
index 6c52612bb..eeb6bac00 100644
--- a/tests/app/main/test_errorhandlers.py
+++ b/tests/app/main/test_errorhandlers.py
@@ -51,8 +51,8 @@ def test_csrf_returns_400(logged_in_client, mocker):
 
     assert response.status_code == 400
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
-    assert page.h1.string.strip() == 'Something went wrong, please go back and try again.'
-    assert page.title.string.strip() == 'Bad request – GOV.UK Notify'
+    assert page.h1.string.strip() == 'Sorry, there’s a problem with GOV.UK Notify'
+    assert page.title.string.strip() == 'Sorry, there’s a problem with the service – GOV.UK Notify'
 
 
 def test_csrf_redirects_to_sign_in_page_if_not_signed_in(client, mocker):
@@ -70,5 +70,5 @@ def test_405_returns_something_went_wrong_page(client, mocker):
 
     assert response.status_code == 405
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
-    assert page.h1.string.strip() == 'Something went wrong, please go back and try again.'
-    assert page.title.string.strip() == 'Bad request – GOV.UK Notify'
+    assert page.h1.string.strip() == 'Sorry, there’s a problem with GOV.UK Notify'
+    assert page.title.string.strip() == 'Sorry, there’s a problem with the service – GOV.UK Notify'
diff --git a/tests/app/main/views/test_uploads.py b/tests/app/main/views/test_uploads.py
index b4d1c9804..081e2fe35 100644
--- a/tests/app/main/views/test_uploads.py
+++ b/tests/app/main/views/test_uploads.py
@@ -504,6 +504,7 @@ def test_uploaded_letter_preview_image_400s_for_bad_page_type(
         file_id=fake_uuid,
         service_id=SERVICE_ONE_ID,
         page='foo',
+        _test_page_title=False,
         _expected_status=400,
     )