Hi Salmac
There are cheaper options out there for a triple play package like yours. Telewest are currently offering the same package you're on for £30 a month but this is available to new customers.
My advice is contact Telewest and say that you're leaving them to sign up to Sky, (Digital TV £15 a mth, unlimited phone calls £5 a month, broadband, free - £10 a month + BT line rental £11 a month = £31 - 41 a mth. Basically you can get the same as what you get now nearly £20 cheaper a month.
If their cancellation team don't offer you a better deal, (my guess is they'll match the Sky offer) then you can switch to Sky anyway and make an instant saving.
Let me know how you get on?
Cheers
Jason