BT still haven't finished their 21CN upgrade..
http://www.btplc.com/21CN/Theroadto2...milestones.htm
This brings speeds upto 24Mb (although most LLU providers already offer this).. of course you need to be near the exchange to have any chance of an improvement. I wouldn't expect BT's next super duper 40Mb service to be available for the majority for the next 10+ years.