NTL is quite a good service to use. You don't have to have cable as long as you have a BT line.
You buy a NTL connector box to plug into your phone socket (it costs £10 on your first phone bill with NTL). They give you a password and a dial code and bobs your uncle! As long as you spend £10 a month on non-internet phone calls with the NTL box or dial code you then get "totally" free internet access. The internet access cuts off after 5 mins if you do not use it and also cuts off after 2 hours of continuous use, but then you just log back on straight away. There never seems to be any problems accessing the net (sometimes a little slow).
Visit
www.ntlworld.com for better details.
I have used various isps and so far this is the best by far>