Location is a bit rubbish but a lot of speed test sites, afaik, do quick ping tests to locate the nearest server and then set that as the default option.
When I first got hooked up to BT, everything suggested I was somewhere in Leed's, speedtest.net would decide Manchester would be the best server to use, if I went with a London server(I'm in London) then the ping was considerably higher, as was pinging various websites based in london, or game servers.
It would seem BT's rather, insane routing had me leaving the BT network in leeds/manchester somewhere, then probably at the end of the 10 days, it flipped back to London being the default option on speedtests, and I also got lower pings to London than Manchester, so they sorted out the routing it would seem as I was as I should be, leaving the BT network in London at the closest(hopefully) possible point.
I don't think IP location is particularly valid, but default servers on speed tests coupled with pinging various websites known to be in certain locations might give you an indication of what ridiculous stuff BT is up to. If you've just been connected, either wait a bit and see if it resolves itself, or e-mail BT and ask if they can do something about it I guess.
