Comment by entuno

Also depends on the size of your fuel tank and how full it already is. The time taken to refuel is (almost) the same regardless, but if you've got a 40l fuel tank vs a 70l one or you're only half-empty then it's going to be less worthwhile.

7p cheaper for 10 minutes works out at about minimum wage if you're buying 30 litres, but with a bigger car you could easily be buying twice that, which works out much better.

Although of course you also need to factor in how much fuel you burn driving to the cheaper place, and the extra wear and depreciation on the car. If you take the HMRC standard rate of 45p/mile (which was meant to cover all of that kind of thing, but hasn't been updated for years) then even going a few miles out of your way quickly ends up costing more than it's likely to save.