found this if u want to try it
For security reasons
BT doesn't give out the locations of their exchanges, not very helpful if your interested in these new 24 meg broadband providers and want to know how much bandwith your going to lose due to distance.
However, I jsut discovered a little trick to find them. Goto the Royal mail web page
click here and click on the postcode finder, you'll need to register to use it. Type "British Telecom" in the business name and your town name. It will then list all the exchanges near you.
This is probably old news but I'd thought i would mention it incase anybody was interested/unaware/cared!