It is Which and their tests are usually rubbish
That and the BBC's reporting.
Why don't they get someone who knows their onions to do their testing? That way they can offer sensible advice rather than branding it all a con (which it is, of course, but only in part) and having people whose cars probably rely on super running around on supermarket 95 RON just because it was good enough for Which's Ford Focus.
It seems Which have a policy of making sure their test are carried out by people who haven't got the a clue what they're dealing with.
Kevin
I was a Which? subscriber for years, and relied on their reports for all my major purchases. I didn't follow them regardless, because sometimes it was obvious that what they recommended just wasn't for me. But I always took note of what they said.
Then they started testing computers and the bits that go with them. While I am definitely not a PC wizard, I've been using all sorts of computers both professionally and privately since I left college in 1966. After a couple of Which? PC reviews, I cancelled my subscription, and was left wondering how much crap I had believed and how many crap products I had bought on their recommendation.
The level of expertise demonstrated by the Which? testers was abysmal, and it really wasn't clear to me what they thought people used computers for.
On the other hand, without any technical knowledge whatsoever, I am completely certain that premium fuels are a completely waste of time and money for ordinary road-legal cars.