I'm sure I'm missing something here. BT is the fixed line operator here - surely all that's needed is to make it BT's problem to provide internet access to the population. The vast majority of UK internet connections in any case use BT's wiring and BT's hardware (and even if your ISP has local loop unbundling and you pay someone else for your phone it's still BT's wiring to your house).
Plus there's the blindingly obvious fact that a large chunk of those not experiencing the joys of 2Mb/s ADSL don't actually need or want it. In a recent report OfCom did, 43% of those unconnected said they weren't interested even if it was completely free.
'Course, the way the government's looking at the moment it'll all be scrapped this time next year.