Well, a friend of mine has decided that the recently heightened fuel prices are a little annoying, and so has put together a website to help:
Petrol Watch UK
However, it needs input (as he says, he doesn't live everywhere in the UK!), so if you know your local petrol price then please enter it . The site is fully functional, so once the data is there it will all work.
Hope this helps people once it's got some more data!