I have run every car I have ever owned, since 1989 till now, almost entirely on supermarket fuel. About 400,000 miles in all. I have never had an engine problem, of any kind, in 30 years motoring. I have never had starting problems, rough running or lack of performance. I am sure there are millions of motorist out there in the same boat. No one will ever convince me that supermarket fuel is anything but safe and perfectly adequate for current motor cars.