I also have tesco near work with 99. Use it now and again but prefer Shell fuel stations tbh. Sounds stupid but they are just a bit nicer.
They are nice. Going to a Shell station is somehow a nice experience. They are neat and tidy, the shops are nice and premium, the people are polite, and quite often you will see something nice at one of the pumps.
At one Shell station I went to a year or so ago there were even attendants who offered to fill up the car for me while I look around the shop!
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They aren't there anymore though... Presumably they decided it was a waste of money. Shame.
Was reading a thread earlier where someone said that stuff can cause hesitation.
I think in some places Momentum has more ethanol than VPower or Ultimate. I don't know how much truth there is to that mind you, I heard it a while ago. May even have been on here.