Regarding an ISP, I am hearing good things about Madasafish and Zen, but as Jason pointed out, this does seem to be a universal problem.
By the way, my 8MB adslmax connection has now stabilised at 3MB. Not great by any means, but I think much of this is down to the internal wiring in my house affecting my sync speeds. The thing that I've noticed about being on the service is the absolutely wild fluctuations. Last night at about midnight I was getting 4MB. Earlier at 6pm I was getting 800K. I think the whole adslmax system needs looking at by BT. It's just so full of holes and quirks that it's literally impossible to get a stable connection.
What I'm gonna do next year once I can contract away from Pipex is activate another phone line that I've got in the house and use it solely for broadband. I'll get good sync speeds then and should have a much better connection.
Best
YC