Come 2010, when the Anglia region switches over entirely to digital, you'll probably get a descent signal. Until then, DTV is only available at a low power from a few main transmitters.
You might also want to try the digital reception predictor part way down this page:
http://www.wolfbane.com/articles/tvr.htm
It will give you the option of several transmitters and you can compare it with analogue reception.