diff --git a/app/main/views/send.py b/app/main/views/send.py
index 21fb7bf32..84100af2d 100644
--- a/app/main/views/send.py
+++ b/app/main/views/send.py
@@ -21,7 +21,6 @@ from notifications_utils.recipients import (
     optional_address_columns,
 )
 from orderedset import OrderedSet
-from werkzeug.routing import RequestRedirect
 from xlrd.biffh import XLRDError
 from xlrd.xldate import XLDateError
 
@@ -135,18 +134,13 @@ def send_messages(service_id, template_id):
                 Spreadsheet.from_file(form.file.data, filename=form.file.data.filename).as_dict,
                 current_app.config['AWS_REGION']
             )
-            if 'file_uploads' not in session:
-                session['file_uploads'] = {}
-            session['file_uploads'].update({
-                upload_id: {
-                    "template_id": template_id,
-                    "original_file_name": form.file.data.filename
-                }
-            })
-            return redirect(url_for('.check_messages',
-                                    service_id=service_id,
-                                    upload_id=upload_id,
-                                    template_type=template.template_type))
+            return redirect(url_for(
+                '.check_messages',
+                service_id=service_id,
+                upload_id=upload_id,
+                template_id=template.id,
+                original_file_name=form.file.data.filename,
+            ))
         except (UnicodeDecodeError, BadZipFile, XLRDError):
             flash('Couldn’t read {}. Try using a different file format.'.format(
                 form.file.data.filename
@@ -480,16 +474,7 @@ def send_test_preview(service_id, template_id, filetype):
     return TemplatePreview.from_utils_template(template, filetype, page=request.args.get('page'))
 
 
-def _check_messages(service_id, template_type, upload_id, preview_row, letters_as_pdf=False):
-
-    if not session.get('file_uploads', {}).get(upload_id):
-        # if we just return a `redirect` (302) object here, we'll get errors when we try and unpack in the
-        # check_messages route - so raise a werkzeug.routing redirect to ensure that doesn't happen.
-
-        # NOTE: this is a 301 MOVED PERMANENTLY (httpstatus.es/301), so the browser will cache this redirect, and it'll
-        # *always* happen for that browser. _check_messages is only used by endpoints that contain `upload_id`, which
-        # is a one-time-use id (that ties to a given file in S3 that is already deleted if it's not in the session)
-        raise RequestRedirect(url_for('main.choose_template', service_id=service_id))
+def _check_messages(service_id, template_id, upload_id, preview_row, letters_as_pdf=False):
 
     users = user_api_client.get_users_for_service(service_id=service_id)
 
@@ -497,29 +482,35 @@ def _check_messages(service_id, template_type, upload_id, preview_row, letters_a
     remaining_messages = (current_service['message_limit'] - sum(stat['requested'] for stat in statistics.values()))
 
     contents = s3download(service_id, upload_id)
+
+    db_template = service_api_client.get_service_template(
+        service_id,
+        str(template_id),
+    )['data']
+
     email_reply_to = None
     sms_sender = None
-    if template_type == 'email':
+    if db_template['template_type'] == 'email':
         email_reply_to = get_email_reply_to_address_from_session(service_id)
-    elif template_type == 'sms':
+    elif db_template['template_type'] == 'sms':
         sms_sender = get_sms_sender_from_session(service_id)
     template = get_template(
         service_api_client.get_service_template(
             service_id,
-            session['file_uploads'][upload_id].get('template_id')
+            str(template_id),
         )['data'],
         current_service,
         show_recipient=True,
         letter_preview_url=url_for(
             '.check_messages_preview',
             service_id=service_id,
-            template_type=template_type,
+            template_id=template_id,
             upload_id=upload_id,
             filetype='png',
             row_index=preview_row,
         ) if not letters_as_pdf else None,
         email_reply_to=email_reply_to,
-        sms_sender=sms_sender
+        sms_sender=sms_sender,
     )
     recipients = RecipientCSV(
         contents,
@@ -550,7 +541,9 @@ def _check_messages(service_id, template_type, upload_id, preview_row, letters_a
     elif preview_row > 2:
         abort(404)
 
-    original_file_name = session['file_uploads'][upload_id].get('original_file_name')
+    if 'file_uploads' not in session:
+        session['file_uploads'] = {}
+    session['file_uploads'][upload_id] = {}
 
     if any(recipients) and not recipients.has_errors:
         session['file_uploads'][upload_id]['notification_count'] = len(recipients)
@@ -565,7 +558,7 @@ def _check_messages(service_id, template_type, upload_id, preview_row, letters_a
         row_errors=get_errors_for_csv(recipients, template.template_type),
         count_of_recipients=len(recipients),
         count_of_displayed_recipients=len(list(recipients.displayed_rows)),
-        original_file_name=original_file_name,
+        original_file_name=request.args.get('original_file_name'),
         upload_id=upload_id,
         form=CsvUploadForm(),
         remaining_messages=remaining_messages,
@@ -582,13 +575,14 @@ def _check_messages(service_id, template_type, upload_id, preview_row, letters_a
     )
 
 
-@main.route("/services/<service_id>/<template_type>/check/<upload_id>", methods=['GET'])
-@main.route("/services/<service_id>/<template_type>/check/<upload_id>/row-<int:row_index>", methods=['GET'])
+@main.route("/services/<service_id>/<uuid:template_id>/check/<upload_id>", methods=['GET'])
+@main.route("/services/<service_id>/<uuid:template_id>/check/<upload_id>/row-<int:row_index>", methods=['GET'])
 @login_required
 @user_has_permissions('send_messages', restrict_admin_usage=True)
-def check_messages(service_id, template_type, upload_id, row_index=2):
+def check_messages(service_id, template_id, upload_id, row_index=2):
+    db_template = service_api_client.get_service_template(service_id, template_id)['data']
 
-    data = _check_messages(service_id, template_type, upload_id, row_index)
+    data = _check_messages(service_id, db_template['id'], upload_id, row_index)
 
     if (
         data['recipients'].too_many_rows or
@@ -611,16 +605,22 @@ def check_messages(service_id, template_type, upload_id, row_index=2):
     return render_template('views/check/ok.html', **data)
 
 
-@main.route("/services/<service_id>/<template_type>/check/<upload_id>.<filetype>", methods=['GET'])
-@main.route("/services/<service_id>/<template_type>/check/<upload_id>/row-<int:row_index>.<filetype>", methods=['GET'])
+@main.route(
+    "/services/<service_id>/<uuid:template_id>/check/<upload_id>.<filetype>",
+    methods=['GET'],
+)
+@main.route(
+    "/services/<service_id>/<uuid:template_id>/check/<upload_id>/row-<int:row_index>.<filetype>",
+    methods=['GET'],
+)
 @login_required
 @user_has_permissions('send_messages')
-def check_messages_preview(service_id, template_type, upload_id, filetype, row_index=2):
+def check_messages_preview(service_id, template_id, upload_id, filetype, row_index=2):
     if filetype not in ('pdf', 'png'):
         abort(404)
 
     template = _check_messages(
-        service_id, template_type, upload_id, row_index, letters_as_pdf=True
+        service_id, template_id, upload_id, row_index, letters_as_pdf=True
     )['template']
     return TemplatePreview.from_utils_template(template, filetype)
 
@@ -645,7 +645,7 @@ def start_job(service_id, upload_id):
         upload_id,
         service_id,
         upload_data.get('template_id'),
-        upload_data.get('original_file_name'),
+        request.args.get('original_file_name'),
         upload_data.get('notification_count'),
         scheduled_for=request.form.get('scheduled_for', '')
     )
@@ -712,12 +712,6 @@ def make_and_upload_csv_file(service_id, template):
         ).as_dict,
         current_app.config['AWS_REGION'],
     )
-    if 'file_uploads' not in session:
-        session['file_uploads'] = {}
-    session['file_uploads'][upload_id] = {
-        "template_id": template.id,
-        "original_file_name": current_app.config['TEST_MESSAGE_FILENAME']
-    }
     return redirect(url_for(
         '.check_messages',
         upload_id=upload_id,
diff --git a/app/templates/views/check/ok.html b/app/templates/views/check/ok.html
index 3e895f404..551a32405 100644
--- a/app/templates/views/check/ok.html
+++ b/app/templates/views/check/ok.html
@@ -27,7 +27,7 @@
   {{ template|string }}
 
   <div class="bottom-gutter-3-2">
-    <form method="post" enctype="multipart/form-data" action="{{url_for('main.start_job', service_id=current_service.id, upload_id=upload_id)}}" class='page-footer'>
+    <form method="post" enctype="multipart/form-data" action="{{url_for('main.start_job', service_id=current_service.id, upload_id=upload_id, original_file_name=original_file_name)}}" class='page-footer'>
       <input type="hidden" name="csrf_token" value="{{ csrf_token() }}" />
       <input type="hidden" name="help" value="{{ '3' if help else 0 }}" />
       {% if choose_time_form and template.template_type != 'letter' %}
@@ -39,7 +39,7 @@
       {% if template.template_type != 'letter' or not request.args.from_test %}
       <button type="submit" class="button">Send {{ count_of_recipients }} {{ message_count_label(count_of_recipients, template.template_type, suffix='') }}</button>
       {% else %}
-        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download class="button">Download as a printable PDF</a>
+        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_id=template.id, upload_id=upload_id, filetype='pdf') }}" download class="button">Download as a printable PDF</a>
       {% endif %}
       <a href="{{ back_link }}" class="page-footer-back-link">Back</a>
     </form>
@@ -63,7 +63,7 @@
             {% if (item.index + 2) == preview_row %}
               {{ item.index + 2 }}
             {% else %}
-              <a href="{{ url_for('.check_messages', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, row_index=(item.index + 2)) }}">{{ item.index + 2 }}</a>
+              <a href="{{ url_for('.check_messages', service_id=current_service.id, template_id=template.id, upload_id=upload_id, row_index=(item.index + 2)) }}">{{ item.index + 2 }}</a>
             {% endif %}
           </span>
         {% endcall %}
diff --git a/app/templates/views/notifications/check.html b/app/templates/views/notifications/check.html
index 8619daf79..fc2aee128 100644
--- a/app/templates/views/notifications/check.html
+++ b/app/templates/views/notifications/check.html
@@ -53,7 +53,7 @@
         {% if template.template_type != 'letter' or not request.args.from_test %}
         <button type="submit" class="button">Send 1 {{ message_count_label(1, template.template_type, suffix='') }}</button>
         {% else %}
-          <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download class="button">Download as a printable PDF</a>
+          <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_id=template.id, upload_id=upload_id, filetype='pdf') }}" download class="button">Download as a printable PDF</a>
         {% endif %}
       {% endif %}
       <a href="{{ back_link }}" class="page-footer-back-link">Back</a>
diff --git a/tests/app/main/views/test_send.py b/tests/app/main/views/test_send.py
index dd4541839..0c6795a88 100644
--- a/tests/app/main/views/test_send.py
+++ b/tests/app/main/views/test_send.py
@@ -586,7 +586,7 @@ def test_upload_valid_csv_shows_preview_and_table(
     page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='sms',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         **extra_args
     )
@@ -599,7 +599,7 @@ def test_upload_valid_csv_shows_preview_and_table(
 
     if expected_link_in_first_row:
         assert page.select_one('.table-field-index a')['href'] == url_for(
-            'main.check_messages', service_id=SERVICE_ONE_ID, template_type='sms', upload_id=fake_uuid, row_index=2
+            'main.check_messages', service_id=SERVICE_ONE_ID, template_id=fake_uuid, upload_id=fake_uuid, row_index=2
         )
     else:
         assert not page.select_one('.table-field-index').select_one('a')
@@ -673,7 +673,7 @@ def test_show_all_columns_if_there_are_duplicate_recipient_columns(
     page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='sms',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         _test_page_title=False,
     )
@@ -721,7 +721,7 @@ def test_404_for_previewing_a_row_out_of_range(
     client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='sms',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         row_index=row_index,
         _expected_status=expected_status,
@@ -1443,9 +1443,10 @@ def test_upload_csvfile_with_valid_phone_shows_all_numbers(
         follow_redirects=True
     )
     with logged_in_client.session_transaction() as sess:
-        assert sess['file_uploads'][fake_uuid]['template_id'] == fake_uuid
-        assert sess['file_uploads'][fake_uuid]['original_file_name'] == 'valid.csv'
+        assert 'template_id' not in sess['file_uploads'][fake_uuid]
+        assert 'original_file_name' not in sess['file_uploads'][fake_uuid]
         assert sess['file_uploads'][fake_uuid]['notification_count'] == 53
+        assert sess['file_uploads'][fake_uuid]['valid'] is True
 
     content = response.get_data(as_text=True)
     assert response.status_code == 200
@@ -1517,7 +1518,7 @@ def test_test_message_can_only_be_sent_now(
         'main.check_messages',
         service_id=service_one['id'],
         upload_id=fake_uuid,
-        template_type='sms',
+        template_id=fake_uuid,
         from_test=True
     ))
 
@@ -1552,7 +1553,7 @@ def test_letter_can_only_be_sent_now(
         'main.check_messages',
         service_id=service_one['id'],
         upload_id=fake_uuid,
-        template_type='letter',
+        template_id=fake_uuid,
         from_test=True
     ))
 
@@ -1583,15 +1584,22 @@ def test_create_job_should_call_api(
     with logged_in_client.session_transaction() as session:
         session['file_uploads'] = {
             fake_uuid: {
-                'original_file_name': original_file_name,
                 'template_id': template_id,
                 'notification_count': notification_count,
                 'valid': True
             }
         }
 
-    url = url_for('main.start_job', service_id=service_one['id'], upload_id=job_id)
-    response = logged_in_client.post(url, data={'scheduled_for': when}, follow_redirects=True)
+    response = logged_in_client.post(
+        url_for(
+            'main.start_job',
+            service_id=service_one['id'],
+            upload_id=job_id,
+            original_file_name=original_file_name
+        ),
+        data={'scheduled_for': when},
+        follow_redirects=True,
+    )
 
     assert response.status_code == 200
     assert original_file_name in response.get_data(as_text=True)
@@ -1689,7 +1697,7 @@ def test_should_show_preview_letter_message(
         url_for(
             'main.check_messages_preview',
             service_id=service_id,
-            template_type='letter',
+            template_id=fake_uuid,
             upload_id=fake_uuid,
             filetype=filetype,
             **extra_args
@@ -1716,7 +1724,7 @@ def test_dont_show_preview_letter_templates_for_bad_filetype(
         url_for(
             'main.check_messages_preview',
             service_id=service_one['id'],
-            template_type='letter',
+            template_id=fake_uuid,
             upload_id=fake_uuid,
             filetype='blah'
         )
@@ -1931,7 +1939,7 @@ def test_check_messages_back_link(
         'main.check_messages',
         service_id=fake_uuid,
         upload_id=fake_uuid,
-        template_type='sms',
+        template_id=fake_uuid,
         **extra_args
     ))
     assert response.status_code == 200
@@ -2014,7 +2022,6 @@ def test_check_messages_shows_too_many_messages_errors(
     with logged_in_client.session_transaction() as session:
         session['file_uploads'] = {
             fake_uuid: {
-                'original_file_name': 'valid.csv',
                 'template_id': fake_uuid,
                 'notification_count': 1,
                 'valid': True
@@ -2024,8 +2031,9 @@ def test_check_messages_shows_too_many_messages_errors(
     response = logged_in_client.get(url_for(
         'main.check_messages',
         service_id=fake_uuid,
-        template_type='sms',
-        upload_id=fake_uuid
+        template_id=fake_uuid,
+        upload_id=fake_uuid,
+        original_file_name='valid.csv',
     ))
     assert response.status_code == 200
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
@@ -2062,7 +2070,7 @@ def test_check_messages_shows_trial_mode_error(
     response = logged_in_client.get(url_for(
         'main.check_messages',
         service_id=uuid.uuid4(),
-        template_type='sms',
+        template_id=fake_uuid,
         upload_id=fake_uuid
     ))
     assert response.status_code == 200
@@ -2115,7 +2123,7 @@ def test_check_messages_shows_trial_mode_error_for_letters(
     page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='letter',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         _test_page_title=False,
     )
@@ -2158,9 +2166,10 @@ def test_check_messages_shows_data_errors_before_trial_mode_errors_for_letters(
     page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='letter',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         _test_page_title=False,
+        original_file_name='example.xlsx',
     )
 
     assert normalize_spaces(page.select_one('.banner-dangerous').text) == (
@@ -2196,7 +2205,7 @@ def test_check_messages_column_error_doesnt_show_optional_columns(
     page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='letter',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         _test_page_title=False,
     )
@@ -2234,7 +2243,7 @@ def test_generate_test_letter_doesnt_block_in_trial_mode(
     page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
-        template_type='letter',
+        template_id=fake_uuid,
         upload_id=fake_uuid,
         from_test=True,
         _test_page_title=False,
@@ -2273,7 +2282,7 @@ def test_check_messages_shows_over_max_row_error(
     response = logged_in_client.get(url_for(
         'main.check_messages',
         service_id=fake_uuid,
-        template_type='sms',
+        template_id=fake_uuid,
         upload_id=fake_uuid
     ))
     assert response.status_code == 200
@@ -2313,15 +2322,15 @@ def test_non_ascii_characters_in_letter_recipients_file_shows_error(
         session['file_uploads'] = {
             fake_uuid: {
                 'template_id': fake_uuid,
-                'original_file_name': 'unicode.csv',
             }
         }
 
     response = logged_in_client.get(url_for(
         'main.check_messages',
         service_id=fake_uuid,
-        template_type='letter',
-        upload_id=fake_uuid
+        template_id=fake_uuid,
+        upload_id=fake_uuid,
+        original_file_name='unicode.csv'
     ))
 
     assert response.status_code == 200
@@ -2336,18 +2345,6 @@ def test_non_ascii_characters_in_letter_recipients_file_shows_error(
     assert page.find('span', class_='table-field-error-label').text == u'Can’t include П, е, т or я'
 
 
-def test_check_messages_redirects_if_no_upload_data(logged_in_client, service_one):
-    response = logged_in_client.get(url_for(
-        'main.check_messages',
-        service_id=service_one['id'],
-        template_type='bar',
-        upload_id='baz'
-    ))
-
-    assert response.status_code == 301
-    assert response.location == url_for('main.choose_template', service_id=service_one['id'], _external=True)
-
-
 @pytest.mark.parametrize('existing_session_items', [
     {},
     {'recipient': '07700900001'},
@@ -2660,8 +2657,12 @@ def test_send_notification_shows_email_error_in_trial_mode(
 
 
 @pytest.mark.parametrize('endpoint, extra_args', [
-    ('main.check_messages', {'template_type': 'email', 'upload_id': fake_uuid()}),
-    ('main.send_one_off_step', {'template_id': fake_uuid(), 'step_index': 0}),
+    ('main.check_messages', {
+        'template_id': fake_uuid(), 'upload_id': fake_uuid(), 'original_file_name': 'example.csv'
+    }),
+    ('main.send_one_off_step', {
+        'template_id': fake_uuid(), 'step_index': 0
+    }),
 ])
 @pytest.mark.parametrize('reply_to_address', [
     None,
@@ -2689,12 +2690,7 @@ def test_reply_to_is_previewed_if_chosen(
         session['recipient'] = 'notify@digital.cabinet-office.gov.uk'
         session['placeholders'] = {}
         session['file_uploads'] = {
-            fake_uuid: {
-                'original_file_name': 'example.csv',
-                'template_id': fake_uuid,
-                'notification_count': 1,
-                'valid': True
-            }
+            fake_uuid: {'template_id': fake_uuid}
         }
         session['sender_id'] = reply_to_address
 
@@ -2713,7 +2709,7 @@ def test_reply_to_is_previewed_if_chosen(
 
 
 @pytest.mark.parametrize('endpoint, extra_args', [
-    ('main.check_messages', {'template_type': 'sms', 'upload_id': fake_uuid()}),
+    ('main.check_messages', {'template_id': fake_uuid(), 'upload_id': fake_uuid()}),
     ('main.send_one_off_step', {'template_id': fake_uuid(), 'step_index': 0}),
 ])
 @pytest.mark.parametrize('sms_sender', [
@@ -2767,23 +2763,6 @@ def test_sms_sender_is_previewed(
 
 
 @pytest.mark.parametrize('endpoint, request_type, extra_args', [
-    (
-        'main.check_messages',
-        'GET',
-        {
-            'template_type': 'email',
-            'upload_id': fake_uuid(),
-        }
-    ),
-    (
-        'main.check_messages_preview',
-        'GET',
-        {
-            'template_type': 'email',
-            'upload_id': fake_uuid(),
-            'filetype': 'png'
-        }
-    ),
     (
         'main.start_job',
         'POST',
@@ -2802,6 +2781,7 @@ def test_sms_sender_is_previewed(
 ])
 def test_redirects_to_choose_template_if_no_session_exists_for_upload_id(
     client_request,
+    mock_get_service_email_template,
     endpoint,
     request_type,
     session_data,
@@ -2817,7 +2797,9 @@ def test_redirects_to_choose_template_if_no_session_exists_for_upload_id(
             service_id=SERVICE_ONE_ID,
             **extra_args,
             _expected_status=301,
-            _expected_redirect=url_for('main.choose_template', service_id=SERVICE_ONE_ID, _external=True)
+            _expected_redirect=url_for(
+                'main.send_messages', service_id=SERVICE_ONE_ID, template_id=fake_uuid, _external=True
+            )
         )
     else:
         client_request.post(
@@ -2825,5 +2807,7 @@ def test_redirects_to_choose_template_if_no_session_exists_for_upload_id(
             service_id=SERVICE_ONE_ID,
             **extra_args,
             _expected_status=301,
-            _expected_redirect=url_for('main.choose_template', service_id=SERVICE_ONE_ID, _external=True)
+            _expected_redirect=url_for(
+                'main.choose_template', service_id=SERVICE_ONE_ID, _external=True
+            )
         )