@MEP... I've seen this and similar comments from you a few times. Is this just your opinion, or can you actually back this up with some facts / research ?
Oh... I'm not having a go, I'm actually interested in this... I tend to use supermarket fuels as my own research concluded that standard 95RON fuels from BP/Esso/Shell/Tesco/Morrisons/ASDA all come from exactly the same fuel bunker at Grangemouth (or, your local refinery).
It's only when you get to the 'premium' fuels, 98RON etc, that there are differences due to differing levels of additives and detergents - which have been shown to have zero/negligible effect on non-performance engines - which my 1.4 8v, certainly is not.
I'm lucky enough to have an ASDA, Tesco, Morrisons, and Sainsburys forecourt within a short distance along my route to work - so I will generally always fill up at the cheapest, although it has to be pointed out that when Morrisons is cheapest, I use the Shell across the road from it who price match them.
I haven't noticed any difference in my average MPG when filling up with Supermarket vs big brand fuel, and I always run it almost empty and then tank up.
Anyway, if you have evidence I'm filling my car up with crap and potentially wrecking it, could you post it for all to see ?
Thanks,
Chris.