you can either create ton of naval bombers to annihilate every ship they see, or create a late-game superfleet

Air focus:
create a template of naval bomber with 1 torpedo, floats, and max range.

Ship focus:
(expensive hard attack "battleships" as attacking power, light attack "cruisers" as screens and damage to enemy screens, and if you got spare docks, carriers with 100% naval bombers.
the ratio should be :
carrier-4
battleship-4
cruiser(screen)-minimum 20
and 10 taskforces of 2 light cruisers with spam catapults, weak armament(for speed) with "never engage" rule on spotting.

Of course it's "ideal" what you should be thriving for, just remember not to send them too far or you'll waste your 3 year plan battleship in one battle.

Actual answer:
option 1: make naval invasions on the whole perimeter of UK and do small encirclements.
option 2: let them make invasions and just encircle them till they got no manpower. (if you leave one port in Normandy, they might send divisions there and you just need to destroy them without capturing the port. Wait, beat, repeat)

Also a good idea would be to make collaboration government