Have a look at
http://www.bethere.co.uk/
With ADSL2+ in theory you can get 24 meg, in practice no one gets it. I've got 17 with the highest I know of being about 20, and it can be as low as 2. Totally dependant on a number of factors - distance to exchange and line quality being the most important.
Exactly the same with ADSL but only up to 8 meg, so I'd guess either you are a long way from your local exchange or you have a lousy line (lots of noise etc.)