There seem to be some very cheap no-catch offers in areas where providers can provide their own service thanks to Local Loop Unbundling (LLU), rather than having to pay BT Wholesale (e.g.
this article on ADSLguide.org.uk). However, there also seem to be plenty of companies offering services at close to - or even below - wholesale prices. This shouts "what's the catch" to me, because it's hard to see how they can make money...