The Germans probably do a series of things that help.
- Introduce 4 rotor enigma. Maybe a different one for various services.
- Germans could be quiet chatty. Many things sent over air waves that could be sent by courier or land line. For example, at one time they sent an entire seasonal war plan for full army group by radio. Easy to stop.
- Send a lot more fake messages.
- Likely try some big victory if UK does not know Germany knows. We have to suppose when the Germans find out, but as a part of deception plan, it could be quiet effective. For example, like we did with Patton, imagine fake messages that make it look like Turkey is about to join war and invade Cyprus and other areas. Make fake German units look like they are staging to be moved to help Turkey. But then attack with units in North Africa.
Or LW was chatty, so send messages greatly exaggerating damage to factories and weakness of German fighter commands to spring a big trap.
Or if timing right, give fake go code on Sea Lion with a few easily recallable units moving.
- There are lots of little things that can be done once a party understand they have compromised communications.