We do already have different implementations of TLS/HTTPS used for different purposes. They're called cipher suites. There are already weaker cipher suites in widespread use, which are the cause of most of the big security issues with TLS/SSL/HTTPS. (This is pretty good article on the subject: http://blog.cryptographyengineering.com/2015/03/attack-of-we...)
I'd guess all the UK government would do is insist that, by law, all secured P2P messaging goes via a given cipher suite (one with a government backdoor/decryption key and, I guess, no perfect forward secrecy).
It's pretty conclusive how bad an idea it is, when all of the leading security experts in the world have said that this is impossible without weakening the entire security of the system.
I'd guess all the UK government would do is insist that, by law, all secured P2P messaging goes via a given cipher suite (one with a government backdoor/decryption key and, I guess, no perfect forward secrecy).
It's pretty conclusive how bad an idea it is, when all of the leading security experts in the world have said that this is impossible without weakening the entire security of the system.