I use ntl freedom. You pay £15 per month which includes phone calls and get free unlimited 24/7 internet. So if you make £15 worth of calls per month you get free internet access, if you make more calls you pay appropriately. If you only make, say, £12 worth of calls you're paying the extra £3 for the internet. (You still pay std line rental to BT)
Link:
https://secure.ntlfreedom.com/(kaz0f....aspx?scid=olr Its the top choice, freedom classic.