diff --git a/app/celery/tasks.py b/app/celery/tasks.py
index b3f090127..a3bc23f5a 100644
--- a/app/celery/tasks.py
+++ b/app/celery/tasks.py
@@ -24,7 +24,7 @@ from sqlalchemy.exc import SQLAlchemyError
 from app.aws import s3
 from datetime import datetime
 from utils.template import Template
-from utils.recipients import RecipientCSV
+from utils.recipients import RecipientCSV, validate_phone_number, format_phone_number
 
 
 @notify_celery.task(name="delete-verify-codes")
@@ -219,7 +219,9 @@ def send_sms(service_id, notification_id, encrypted_notification, created_at):
 
 
 def allowed_send_to_number(service, to):
-    if service.restricted and to not in [user.mobile_number for user in service.users]:
+    if service.restricted and format_phone_number(validate_phone_number(to)) not in [
+        format_phone_number(validate_phone_number(user.mobile_number)) for user in service.users
+    ]:
         return False
     return True
 
diff --git a/tests/app/celery/test_tasks.py b/tests/app/celery/test_tasks.py
index bb2a7bb3b..b229a5f37 100644
--- a/tests/app/celery/test_tasks.py
+++ b/tests/app/celery/test_tasks.py
@@ -296,13 +296,13 @@ def test_should_send_sms_without_personalisation(sample_template, mocker):
 
 
 def test_should_send_sms_if_restricted_service_and_valid_number(notify_db, notify_db_session, mocker):
-    user = sample_user(notify_db, notify_db_session, mobile_numnber="+441234123123")
+    user = sample_user(notify_db, notify_db_session, mobile_numnber="07700 900890")
     service = sample_service(notify_db, notify_db_session, user=user, restricted=True)
     template = sample_template(notify_db, notify_db_session, service=service)
 
     notification = {
         "template": template.id,
-        "to": "+441234123123"
+        "to": "+447700900890"  # The user’s own number, but in a different format
     }
     mocker.patch('app.encryption.decrypt', return_value=notification)
     mocker.patch('app.firetext_client.send_sms')
@@ -317,17 +317,17 @@ def test_should_send_sms_if_restricted_service_and_valid_number(notify_db, notif
         now.strftime(DATETIME_FORMAT)
     )
 
-    firetext_client.send_sms.assert_called_once_with("+441234123123", "Sample service: This is a template")
+    firetext_client.send_sms.assert_called_once_with("+447700900890", "Sample service: This is a template")
 
 
 def test_should_not_send_sms_if_restricted_service_and_invalid_number(notify_db, notify_db_session, mocker):
-    user = sample_user(notify_db, notify_db_session, mobile_numnber="+441234123123")
+    user = sample_user(notify_db, notify_db_session, mobile_numnber="07700 900205")
     service = sample_service(notify_db, notify_db_session, user=user, restricted=True)
     template = sample_template(notify_db, notify_db_session, service=service)
 
     notification = {
         "template": template.id,
-        "to": "+440000000000"
+        "to": "07700 900849"
     }
     mocker.patch('app.encryption.decrypt', return_value=notification)
     mocker.patch('app.firetext_client.send_sms')