The Sitefinder site has had a major revamp. It now lets you find your local mast using Google Maps and street view.

http://www.sitefinder.ofcom.org.uk/

It's so much better now.

The old map was a real pain to use.

i have a three fone and where i live the signal is crap but apparently its near me?

Maybe there is something wrong with the Three mast near you? Have you tried customer services?

When I enter my postcode it appears Vodaphone have a mast situated in the Thames.