Call their bluff.
Close all local UK operations, so that no employees or corporate officers can be arrested.
Refuse to comply, and dare them to geoblock. Without Google and Apple, the UK economy would probably collapse. It isn't so much that those services are crucial (although they are), it's that Britain is already on the fiscal brink and all it would really take is a little push.
I'm sure blocking the Internet would go over really well with the British people, too.
NEW: U.K. advances proposal to force Apple, Google, Signal, & other platforms to scan private content on usersโ devices โ executives could face prison if they refuse.