Typical BT

penrhyn

I'd think long and hard before moving your fixed line rental away from BT.
When you do this it will BT who will be called in to maintain or repair your line, so rather than going directly to them you would have to go via your new service provider.
Companies like Talk Talk will give you a complete line rental/phone broadband package, but will not allow you to move your broadband away from them if you happen to see a better deal.
Most providers insist that you have a BT land line in the first place, so that would cost you another £125 to reconnect.

Just a friendly thought.