Is supermarket fuel inferior to petrol station fuel?

It was recently suggested to me that fuel obtained from supermarkets is inferior to that obtained from filling stations and service areas and is “diluted” in some way, resulting in lower performance and mpg. I have observed many and various tankers filling up tanks at supermarkets and fail to acknowledge the veracity of the above statement in view of the necessary compliance with British Standards. Do you have any comments please?

Asked on 30 November 2013 by VW, Derby.

Answered by Honest John
Yes. I get 9 per cent better fuel economy from Shell V-Power Nitro Plus, for a price premium of 5.7 per cent. Probably thanks to the 99Ron, which gives more torque at lower rpm allowing the car to run cleanly at lower revs so I can change up earlier, and partly because of the V-Power additive package that you don't get in supermarket fuel, wherever it came from.
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