i believe areas which are analogue only are:
parts of southampton
parts of leicester
central london & westminster
milton keynes.
the southampton parts and the leicester parts could be reletively easy to upgrade, as no major digging up the road etc, would have to be done. please correct me if i'm wrong.
but, central london, westminster and milton keynes needs major works done, i think much of the cabling has to be re-laid. so lots of money would be needed. telewest don't have this situation; eurobell areas for example need new equipment, not new cabling - much cheaper.
plus, ntl are spending a lot of money on upgrading ex-videotron areas in london. so that'll have to be finished before ntl move onto something else.
i think ntl should start migrating analogue customers to digital (where possible), offering discounted prices and the like. also, i think ntl should remove all premium content on analogue (like sky movies, disney etc) to free up more capacity for the digital network.