One other thing - be a bit careful about going for the very cheapest supplier.
It is possible to get ADSL for less than £20 quid a month
including VAT, but BT charges the ISP around £15 per month per user. This means the ISP is trying to provide a service
and make a profit off no more than a couple of quid per customer per month - assuming they can survive on that the support you get is minimal. Better to pay a couple of quid more and get a bit of service IMHO.
More expensive is not always better, of course, and most people would agree that you can save a fiver a month off BT Openworld's price without any loss in service or quality. Pipex is one example, but there are several others - have a look at the ratings on
http://www.adslguide.org.uk/ and decide.
