The possibility of encryption of the TV services has been discussed numerous times over that last 20 or so years. There was even work done on analogue video encryption in the early 90's using line shuffling and rotation techniques similar to what Sky were using on their analogue platform at the time (BBC Select).

I was at Uni just at the time digital terrestrial TV was launched in the UK and there were many discussions on how that would be the right time to begin encryption of these services. Certainly under the reign of OnDigital and ITV digital this could'be been possible since 100% of the recivers in use at that time had the necessary CI slots and the platform owner had CRM infrastructure in place. However, since they went royally tits up the proliferation of CI-less boxes and TV's in the market has made something like much more difficult to achieve without people having to fork out more money. Also, the cost saved in 'policing' the licence would then need to piled into making sure customer accounts are looked after and ensuring the encryption systems aren't bypassed.

However, if the BBC did go the encryption route I'm 100% sure they would use a system that allowed people to use CAM's in whatever system they wanted (ie. a linux box), unlike Sky who make sure you're tied into their hardware.

However, you've still got to figure out a way of encrypting all the FM radio services as well as protecting all the online material being read by foreigners or people who haven't paid their dues!