All of which is completely irrelevant.
To be able to sell fuel in the UK, it has to be of a certain quality. For regular petrol it's BS 228:2012, and for super unleaded that quality is BS 7800:2006. Those are very strict standards set by some very clever people who have to protect the equipment used by not only Joe Bloggs, but also of the civil service as well. In short, it's not worth their while making a crap standard. BS numbers are some of the highest quality checks anywhere in the world, hence why people usually want to buy British products.
Anyways, by buying fuel in the UK from anywhere other than Pikey Ted's Good Ol' Petrol Place, it HAS to meet either of those BS numbers. As long as it does, then that's all you need to worry about. If it exceeds it then great, that's a bonus, but the standard alone is more than enough to give a quality indicator.