the fuel industry work in a system called a cartel, where they discuss between themselves and roughly set the price. although they can't admit this as its highly illegal.
bit like what the oil industry do as well.
and even on the forecourts.
i used to work for sainsburys petrol station as a student and we used to ring round all the local garages to find out their price, and vice versa we used to get phone calls asking the same question. although no one would say they were calling from another petrol station, everybody knew who it was.
fuel isn't standardised either. you could pick 20 bp garages around the country and it would be unlikely to find the fuel at the same price at any of them.
if an area is affluent, then they charge more. same with food prices as well
which ever way you look at it we get screwed. i use tesco because it close and its cheap. i used to use BP which is next door to tesco, but its more expensive. and as for points i was collecting nectar, but am currently doing clubcard as the points are paying for 2 nights in a hotel for my brothers wedding.