Ok maybe on the BP ultimate I will stand corrected but between tesco and vpower I doubt there's much in it
Would be inclined to agree - don't think the difference would be at all noticeable.
I've read fuel is supposed to start to loose it's octane rating the longer its sat - I tend to think the best option is not the brand tesco/shell, but whichever station shifts the most and should therefore have fresher fuel. I also imagine the lines would be kept cleaner having more fuel flowing through them too...
Not sure exactly how much (if at all) difference it actually makes, but could go some way to explaining the 'bad batches' of fuel people claim to have had from time to time...

