The tax on a litre is probably more than 69p anyway.
Think the other problem is that people are too selfish to stick with it and if the price dropped on BP's fuel by 2p then people would cave in and use BP again. It's the same with road tax, if everyone refused to pay for road tax, how could the government possibly enforce it? Some people would inevitably have their cars crushed but eventually the government would stop being a**eholes. A majority of people won't take the risk tho, a curse of being British. Americans wouldn't stand for any of it. . .