diff --git a/app/celery/research_mode_tasks.py b/app/celery/research_mode_tasks.py
index 5fbe09b01..b03d8ee69 100644
--- a/app/celery/research_mode_tasks.py
+++ b/app/celery/research_mode_tasks.py
@@ -1,3 +1,4 @@
+import random
 from datetime import datetime, timedelta
 import json
 
@@ -125,8 +126,8 @@ def create_fake_letter_response_file(self, reference):
     now = datetime.utcnow()
     dvla_response_data = '{}|Sent|0|Sorted'.format(reference)
 
-    # try and find a filename that hasn't been taken yet - going back in time 60 seconds
-    for i in range(30):
+    # try and find a filename that hasn't been taken yet - from a random time within the last 30 seconds
+    for i in sorted(range(30), key=lambda _: random.random()):
         upload_file_name = 'NOTIFY-{}-RSP.TXT'.format((now - timedelta(seconds=i)).strftime('%Y%m%d%H%M%S'))
         if not file_exists(current_app.config['DVLA_RESPONSE_BUCKET_NAME'], upload_file_name):
             break
diff --git a/tests/app/celery/test_research_mode_tasks.py b/tests/app/celery/test_research_mode_tasks.py
index aacfd81d5..7a00f7163 100644
--- a/tests/app/celery/test_research_mode_tasks.py
+++ b/tests/app/celery/test_research_mode_tasks.py
@@ -15,7 +15,13 @@ from app.celery.research_mode_tasks import (
     ses_notification_callback,
     create_fake_letter_response_file,
 )
-from tests.conftest import set_config_values
+from tests.conftest import set_config_values, Matcher
+
+
+dvla_response_file_matcher = Matcher(
+    'dvla_response_file',
+    lambda x: 'NOTIFY-20180125140000-RSP.TXT' < x <= 'NOTIFY-20180125140030-RSP.TXT'
+)
 
 
 def test_make_mmg_callback(notify_api, rmock):
@@ -108,12 +114,11 @@ def test_failure_firetext_callback(phone_number):
     }
 
 
-@freeze_time("2018-01-25 14:00:00")
+@freeze_time("2018-01-25 14:00:30")
 def test_create_fake_letter_response_file_uploads_response_file_s3(
         notify_api, mocker):
     mocker.patch('app.celery.research_mode_tasks.file_exists', return_value=False)
     mock_s3upload = mocker.patch('app.celery.research_mode_tasks.s3upload')
-    filename = 'NOTIFY-20180125140000-RSP.TXT'
 
     with requests_mock.Mocker() as request_mock:
         request_mock.post(
@@ -128,16 +133,15 @@ def test_create_fake_letter_response_file_uploads_response_file_s3(
             filedata='random-ref|Sent|0|Sorted',
             region=current_app.config['AWS_REGION'],
             bucket_name=current_app.config['DVLA_RESPONSE_BUCKET_NAME'],
-            file_location=filename
+            file_location=dvla_response_file_matcher
         )
 
 
-@freeze_time("2018-01-25 14:00:00")
+@freeze_time("2018-01-25 14:00:30")
 def test_create_fake_letter_response_file_calls_dvla_callback_on_development(
         notify_api, mocker):
     mocker.patch('app.celery.research_mode_tasks.file_exists', return_value=False)
     mocker.patch('app.celery.research_mode_tasks.s3upload')
-    filename = 'NOTIFY-20180125140000-RSP.TXT'
 
     with set_config_values(notify_api, {
         'NOTIFY_ENVIRONMENT': 'development'
@@ -154,11 +158,22 @@ def test_create_fake_letter_response_file_calls_dvla_callback_on_development(
             assert request_mock.last_request.json() == {
                 "Type": "Notification",
                 "MessageId": "some-message-id",
-                "Message": '{"Records":[{"s3":{"object":{"key":"' + filename + '"}}}]}'
+                "Message": ANY
+            }
+            assert json.loads(request_mock.last_request.json()['Message']) == {
+                "Records": [
+                    {
+                        "s3": {
+                            "object": {
+                                "key": dvla_response_file_matcher
+                            }
+                        }
+                    }
+                ]
             }
 
 
-@freeze_time("2018-01-25 14:00:00")
+@freeze_time("2018-01-25 14:00:30")
 def test_create_fake_letter_response_file_does_not_call_dvla_callback_on_preview(
         notify_api, mocker):
     mocker.patch('app.celery.research_mode_tasks.file_exists', return_value=False)
@@ -181,15 +196,15 @@ def test_create_fake_letter_response_file_tries_to_create_files_with_other_filen
     create_fake_letter_response_file('random-ref')
 
     assert mock_file_exists.mock_calls == [
-        call('test.notify.com-ftp', 'NOTIFY-20180125140030-RSP.TXT'),
-        call('test.notify.com-ftp', 'NOTIFY-20180125140029-RSP.TXT'),
-        call('test.notify.com-ftp', 'NOTIFY-20180125140028-RSP.TXT'),
+        call('test.notify.com-ftp', dvla_response_file_matcher),
+        call('test.notify.com-ftp', dvla_response_file_matcher),
+        call('test.notify.com-ftp', dvla_response_file_matcher),
     ]
     mock_s3upload.assert_called_once_with(
         filedata=ANY,
         region=ANY,
         bucket_name=ANY,
-        file_location='NOTIFY-20180125140028-RSP.TXT'
+        file_location=dvla_response_file_matcher
     )
 
 
diff --git a/tests/conftest.py b/tests/conftest.py
index ee47643ce..e3762afd9 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -162,3 +162,15 @@ def set_config_values(app, dict):
     finally:
         for key in dict:
             app.config[key] = old_values[key]
+
+
+class Matcher:
+    def __init__(self, description, key):
+        self.description = description
+        self.key = key
+
+    def __eq__(self, other):
+        return self.key(other)
+
+    def __repr__(self):
+        return '<Matcher: {}>'.format(self.description)