bb2002, when amanoffewwords says that Telewest is the "only" broadband provider, I think he means that once you've tried them you'd never go back to DSL/ADSL. The cable service is superb, and they have given us our second free upgrade in the past few months. Our 2mb connection went to 3mb, and now 4mb, for £50/month (expensive, but reasonable at the speeds we're now getting). All the Telewest services are unmetered (no usage cap) and you can't get such speeds anywhere else at the moment unless you live in central london and sign up to Bulldog DSL; and even then the Bulldog speed is "variable" in tune with peak/offpeak times of the day.
The support on Telewest is very reliable and with every package you get 30mb webspace (not much, admittedly, but has full Frontpage extensions support) and 5 large mailboxes with 5 addresses each, and for £4 a month you can take the webspace up to 100mb with full scripting (ASP/PHP/CGI/etc) support, if you need that kind of thing.
Unfortunately cable seems to be available in only a select few areas
I'd try not to go with NTL, my relatives have had a lot of trouble with them (unreliable, sometimes capped service).