This is not specifically a classic car issue, although we all want to preserve our ancient engines as long as possible. Most Saturdays I read Honest John's column in the Telegraph, and he's always banging on about how supermarket petrol doesn't have any detergents in in it, causing all sorts of problems, whereas Shell and Texaco fuels are the ones of choice. He says it applies to diesel as well - these brands are high lubricity, Tesco etc is not. Last week I asked him what independent tests show the superiority these brands. Guess what? He couldn't cite any, but said it was his experience and that of his readers.
Now if this is a real effect why are these 2 companies not making as much fuss about it as Honest John does? If they are, and I have missed it, they are not doing a very good promotional job. My own experience doesn't support the claim. Our family cars are a Renault Espace and a Citroen ZX TD, on 130k and 140k miles respectively, and both have been run on supermarket fuel almost all their lives. During brief periods on other brands there was no detectable difference, and there have been no problems in any way attributable to fuel quality. The Espace had its head off 2 years ago to replace a gasket and it wasn't particularly coked up. The ZX hasn't been touched apart from cambelt changes.
As I'm just building my Sprite engine I'm wondering if there's anything in this story and whether I should pay extra for the fuel I put in it.