diff --git a/app/celery/broadcast_message_tasks.py b/app/celery/broadcast_message_tasks.py
index a02c6004b..0cdc2800a 100644
--- a/app/celery/broadcast_message_tasks.py
+++ b/app/celery/broadcast_message_tasks.py
@@ -32,7 +32,8 @@ def send_broadcast_event(broadcast_event_id):
 def send_broadcast_provider_message(broadcast_event_id, provider):
     broadcast_event = dao_get_broadcast_event_by_id(broadcast_event_id)
 
-    broadcast_provider_message = create_broadcast_provider_message(broadcast_event, provider)
+    broadcast_provider_message, message_number = create_broadcast_provider_message(broadcast_event, provider)
+    formatted_message_number = format_sequential_number(message_number.broadcast_provider_message_number)
 
     current_app.logger.info(
         f'invoking cbc proxy to send '
@@ -50,6 +51,7 @@ def send_broadcast_provider_message(broadcast_event_id, provider):
     if broadcast_event.message_type == BroadcastEventMessageType.ALERT:
         cbc_proxy_provider_client.create_and_send_broadcast(
             identifier=str(broadcast_provider_message.id),
+            message_number=formatted_message_number,
             headline="GOV.UK Notify Broadcast",
             description=broadcast_event.transmitted_content['body'],
             areas=areas,
@@ -59,6 +61,7 @@ def send_broadcast_provider_message(broadcast_event_id, provider):
     elif broadcast_event.message_type == BroadcastEventMessageType.UPDATE:
         cbc_proxy_provider_client.update_and_send_broadcast(
             identifier=str(broadcast_provider_message.id),
+            message_number=formatted_message_number,
             headline="GOV.UK Notify Broadcast",
             description=broadcast_event.transmitted_content['body'],
             areas=areas,
@@ -69,6 +72,7 @@ def send_broadcast_provider_message(broadcast_event_id, provider):
     elif broadcast_event.message_type == BroadcastEventMessageType.CANCEL:
         cbc_proxy_provider_client.cancel_broadcast(
             identifier=str(broadcast_provider_message.id),
+            message_number=formatted_message_number,
             headline="GOV.UK Notify Broadcast",
             description=broadcast_event.transmitted_content['body'],
             areas=areas,
diff --git a/app/dao/broadcast_message_dao.py b/app/dao/broadcast_message_dao.py
index 281e5b09a..e79f0a8f8 100644
--- a/app/dao/broadcast_message_dao.py
+++ b/app/dao/broadcast_message_dao.py
@@ -58,4 +58,4 @@ def create_broadcast_provider_message(broadcast_event, provider):
         broadcast_provider_message_id=broadcast_provider_message_id)
     db.session.add(provider_message_number)
     db.session.commit()
-    return provider_message
+    return provider_message, provider_message_number
diff --git a/tests/app/celery/test_broadcast_message_tasks.py b/tests/app/celery/test_broadcast_message_tasks.py
index 61aedcdd7..e49db47e7 100644
--- a/tests/app/celery/test_broadcast_message_tasks.py
+++ b/tests/app/celery/test_broadcast_message_tasks.py
@@ -133,6 +133,7 @@ def test_send_broadcast_provider_message_sends_data_correctly(mocker, sample_ser
 
     mock_create_broadcast.assert_called_once_with(
         identifier=str(broadcast_provider_message.id),
+        message_number=mocker.ANY,
         headline='GOV.UK Notify Broadcast',
         description='this is an emergency broadcast message',
         areas=[{
@@ -178,6 +179,7 @@ def test_send_broadcast_provider_message_sends_update_with_references(mocker, sa
 
     mock_update_broadcast.assert_called_once_with(
         identifier=str(broadcast_provider_message.id),
+        message_number=mocker.ANY,
         headline="GOV.UK Notify Broadcast",
         description='this is an emergency broadcast message',
         areas=[{
@@ -223,6 +225,7 @@ def test_send_broadcast_provider_message_sends_cancel_with_references(mocker, sa
 
     mock_cancel_broadcast.assert_called_once_with(
         identifier=str(broadcast_provider_message.id),
+        message_number=mocker.ANY,
         headline="GOV.UK Notify Broadcast",
         description='this is an emergency broadcast message',
         areas=[{
@@ -265,6 +268,7 @@ def test_send_broadcast_provider_message_errors(mocker, sample_service):
 
     mock_create_broadcast.assert_called_once_with(
         identifier=ANY,
+        message_number=mocker.ANY,
         headline="GOV.UK Notify Broadcast",
         description='this is an emergency broadcast message',
         areas=[{
diff --git a/tests/app/dao/test_broadcast_message_dao.py b/tests/app/dao/test_broadcast_message_dao.py
index a8fb160b5..dd5a69ac4 100644
--- a/tests/app/dao/test_broadcast_message_dao.py
+++ b/tests/app/dao/test_broadcast_message_dao.py
@@ -53,7 +53,7 @@ def test_create_broadcast_provider_message_creates_in_correct_state(sample_broad
         transmitted_content={'body': 'Initial content'}
     )
 
-    broadcast_provider_message = create_broadcast_provider_message(broadcast_event, 'fake-provider')
+    broadcast_provider_message, message_number = create_broadcast_provider_message(broadcast_event, 'fake-provider')
 
     assert broadcast_provider_message.status == 'sending'
     assert broadcast_provider_message.broadcast_event_id == broadcast_event.id
diff --git a/tests/app/db.py b/tests/app/db.py
index a0354e894..4dd2ec9d1 100644
--- a/tests/app/db.py
+++ b/tests/app/db.py
@@ -1074,4 +1074,4 @@ def create_broadcast_provider_message(
     db.session.add(provider_message_number)
 
     db.session.commit()
-    return provider_message
+    return provider_message, provider_message_number