It's crazy I must say, in this area certainly BP have the highest prices and Esso is usually a penny or two more than Shell and the supermarket ones as well. I try to only get petrol at Shell as I think their quality is the best. Shell is quite a ~~~~~~~ too in my opnion as they pulled out of a great plan to provide a significant amount of energy to London via an off shore windfarm. Probably won't happen now.
Having said all this, the good thing about high petrol prices is that car manufacturers are now doing their upmost best to only produce cars beyond 50mpg. 70mpg+ isn't too far off to being the norm I'd say.
70% of petrol prices is tax!