It's a complete bugger even if you've got one telly. Either all tellies are getting an upgrade to have some form of authentication scheme to dictate what channels you can view (whether that's the "hardware dongle card" or a web-login interface) - or you're supplying new decoder boxes to everyone that will effectively perform the same function.
In the former case, there's nothing to do as "upgraded" kit will do the authentication thing inherently. In the latter case, just stick the authentication system on the antenna (although perhaps some method of communicating with it would be nice so you don't have to climb a ladder to change credentials).
Massive upheaval, either way.
Of course, if everything moves to IP TV, rather than old-fashioned radio waves, it becomes a lot easier at the domestic end, but requires BT Reacharound to do a lot more work on the country's infrastructure.