Just an update
An engineer arrived and eventually found that a splitter had been added in the little wall mounted box outside my house when my next door neighbour had BB installed a month or so ago.
Apparently his cable feed proved to be faulty when they came to install his BB so they split my cable 'temporarily'. They repaired his link the following day but left the splitter in my cable without a terminator in the now unused socket.
He said he didn't think it was the fact that a terminator hadn't been fitted but more the fact that because this hadn't been fitted that moisture had got in the splitter...hence only some channels dying.
Anyway I don't know how much of that is true but I'm just waiting now to see if I am charged for the Front Row films I couldn't watch.
The good news is the TV is back to normal...thanks NTL for a rapid response