I did quite a lot of research for my Dad re Broadband in the UK - gave me a nice headache but eventually went for the services of
plus.net - the option without the modem cost £18.99 x month + VAT for full-blown unrestricted bband access. Startup cost are quite high but I reckon you save long term.
I'm going down to see my Dad today to hook it up - I'll come back and revise my post if it goes t*ts up.
hth
Charles
ps. Personally I use Telewest Blueyonder - very pleased with it but it's definitely not the cheapest.