I think the idea of everyone boycotting all petrol stations is a no goer, as at the end of the day we will have to refuel at some time. And they know this.
A much better idea, IMO, is to target specific brands. ie, if everybody stopped getting petrol from say BP, making sure they knew the reason was because of the pricing, then it is bound to hit them hard. Surely they would then have to consider lowering their prices to make it a more attractive proposition to us.
If the prices do come down, then a boycott of say, Shell, could be done. At the same time getting fuel from the now lower price of BP. And doing this will force competition between them.
Can you imagine the impact a total boycott of a sole distributor would have? I've no idea how feasible it would be, or wether the goverment would bail them out, but the profits these companies are making DAILY are not to be sniffed at. Imagine a week/months loss of profit.
Viva la revolution!!!
On a side note the boycott of the S*n newspaper within Liverpool has had a huge effect on its profits. From selling 200 - 250,000 papers daily, it is down to less than 50,000. And thats been going on for 16 years. Imagine that on a nationwide scale.