Already Broken?
So if TLS is allowed, presumably they can already read it so we'll be allowed to continue.
All it needs is for all mail servers outside the UK to be reconfigured to insist on secure comms or fail and suddenly a lot of the UK's important business will dry up or revert back to fax machines.
And what about my Android phone, on which I've enabled encryption so even if PC Plod confiscates it, he still won't be able to read it without my knowledge?