Another post mentioned Orange. My exchange is Orange LLU enabled (though I dont really know what that means, no throttling??) The package I would go for is Home Starter at £9.79
I've been on Orange and its predecessors for years.
I find Orange reliable, fast (I'm getting consistent 6.6 Meg download speed on their 8 Meg package) and value-for-money.
However, their support is the pits. They don't listen, are often unintelligible and just sprout from a pre-digested script of "solutions".
Only take Orange if you can manage without their support. The Home Starter package includes a Siemens wireless router which you can set up manually if you know a bit about routers and network connections.
Also be aware that this package includes taking over your phone calls but not your BT phone line, which might clash with your existing contract with BT.