Have a look at http://www.adslguide.org.uk where they compare all current broadband ISP's for speed, cost, user reliability, customer service. They also do a monthly comparison of speed and give you the top 10 (you might need to look through the news archive - last one was June 6). I use Eclipse (reliable and fast); my mate uses Nildram (meant to be good for gamers). Also look at adslguide's news and forums which will keep you up-to-date on any problems or offers.
I'm with BT and have had no trouble at all. They've just sent me a letter saying the price is dropping to, i think, 24.99. They are imposing a download limit, although they claim it will have no effect on my usage (and I use it a lot). However, it's still a liberty I think considering they force you to sign up to a year.
Lads/lasses? (I haven't done a daft bint count), thanks a lot for all your help. BT sounds good, 15mb limit should be no problem for me. I shall bookmark the adsl site. Are there any providers you would avoid?