In addition to what Tony posted, I came across this yesterday.
'Super fuels' a waste of money for most cars | This is Money
According to Which "The standard fuels we tested were all up to the job, whether from a major fuel brand or a supermarket."
"There's no conclusive evidence to show that super fuels are better for your car in the long run – so in a time of high oil prices, why would you choose to pay more?"