The UK Government wants access, when requested, to the end-to-end encrypted messages and data for everyone in the UK. Demanding the impossiblePut simply, restricting end-to-end encryption on a single-country basis is inherently unenforceable. This issue was highlighted when Apple withdrew Advanced Data Protection (ADP) from the UK marketplace back in February. This is not so simple, however: once you enable encryption, to disable it you need to decrypt the data before switching off the encryption, otherwise the encrypted data remains encrypted and unreadable. To enforce it at the border, each person entering the country would need to unencrypt end-to-end encrypted data and disable any apps or features that use end-to-end encryption where there is no backdoor.