Some fuels give more MPG than others in my experience.

This was also backed up by a friend with a modern Mercedes, he complained to the garage about a sudden drop in economy and they told him to avoid supermarkets, and sure enough the economy went back up.

This is also fairy easy to test to see if it affects your machine.

You are not going to do any damage and for the amount
extra it will cost it ain't going to beak the bank, so experiment
a bit see if it runs better or gives more mpg on one or the other.
I seem to remember that BP was supposed to give more mpg not
by burning less fuel as such but by having a lubrication addative
so less friction, that to me would be worth a few pence a fill by
cutting wear on cylinder and pistons or more to the point the fuel
pump and injectors.
My DCi Diesel runs noticeably better on Morrison's supermarket fuel.
It is worth thinking about using Shell supper fuel if you run a older
engine not intended for fuel with Ethanol in it as that fuel supposedly
as less than others, the engines will burn it ok but it attacks the seals
in the fuel system.

from what I have read on inter google and other forums etc...
Base petrol is all the same - comes from the same depot....
The brands secret additives are added to the petrol when its in the tanker, prior to delivery to the forecourt...

But...
The Tesco Momentum and other supermarket or Petrol Station higher RON rated petrol has additives that can improve things like carb icing...
If your engine does not need the anti detonation extras, the higher RON rated petrol can actually give less bang for ya buck!

Opinions vary but having read a lot about this, my view is that super fuels make no difference to the sort of bikes we ride here as far as performance and/or mileage is concerned.

You can only really compare two fuels with any accuracy in a precisely monitored rolling road lab and even then any difference would apply only to the test vehicle and could not be assumed to apply to other makes and models.

Back in the real world it's close to impossible to make a fair comparison between two fuels because of fluctuations in factors like weather, traffic, riding style, state of tune that influence consumption between two test periods. No two rides in normal road conditions will be so exactly the same that they eliminate the influence of such factors.

If you really want to clean your fuel system, try a product called Techron. Its hard to come by as it is made by Texaco/Chevron Petrochemical and not generally available in UK. I got a bottle via an eBay reseller in the Netherlands. Its like Redex on steroids and seems to do the trick. Redex didn't touch my R1's gummed up carbs, then I followed a kiwi forum members advice to use Techron and it worked wonders. It won't clean your piston crowns (nothing will except a strip down and hand scrape) but it will remove varnish etc from fuel injectors and inlet valves.