I've done it - just phoned and called NTL
Will end as of 26th January. Not much of a fight - asked me who I was moving to. Pointed out that I would need a phone line for another provider, and I would have to consider the cost of the line rental when deciding if another provider was cheaper. This isn't actually true - I already have a BT line, and have had for some time, so it's not part of the equation. Sky+ and broadband comes to £21 - a saving of £4 plus I get an extra service (TV).
I phoned Sky. Very strange woman. "Can I upgrade to the medium broadband service - £5 a month", I said. "Did you have a good Christmas - seemed to go quickly?", came the reply
That threw me a bit. Not really supposed to chat to customers. Professionalism and all that. Hmmm. Just have to wait 4hrs and it auto-magically happens
[edit] Stats attached
Faster than NTL