Re: line open
"Right , I'm off to right a ten quid per minute line that never lets anyone hang up....."
No exactly sure what you are saying, but it only works when you call someone not the other way around. So the ten quid a minute line company would have to call you, but they wouldn't make any money on that. If you called it, then the call would clear when you hung up.
One trick could be to make your premium rate service answer the call with a ringing tone so that it sounds like it still hasn't connected and the caller doesn't realise they are being charged for the call.