Stick your postcode into
SamKnows Mapper and then select your road, and you'll find an indication of your likely connection speed for the ADSL and ADSL2 providers available on your exchange.
Many people are switching to O2 (cheap if you use their mobile phone services), Sky (very cheap if you use their TV service) and Be (expanding very, very rapidly -- sooner or later they are almost bound to have problems).