Capture by Germany of French channel harbors forced opening new convoy routes according to the War Cabinet Weekly Résumé No. 45of the Naval, Military and Air Situation 4-12 July 1940

An item reported that due the threat of German air attacks since the capture of the [French] channel harbors were the routes of the convoys by the Royal Navy changed. Outward bound was now north about from Southend, homeward bound via harbors on the West Coast. For coastal trace which needed to pass the Channel was a special convoy of 10 ships available to depart on alternate days from Southend and which was escorted as far as the Island Wight.

Source

National Archive UK. CAB-66-9-42.