Oil company propaganda. The fact is that The U.K is divided up into areas with each area having a major oil refinery in it. For example if like me you live in North Wales then your fuel comes from Stanlow, Ellesmere Port. So, no matter where I fill up, whether it's our local ASDA, Texaco, Shell, BP, etc garage I'll be getting fuel made in Stanlow at The former Shell refinery. If you live on the South Coast your fuel will come from The Esso refinery in Fawley and so on. Just think about it, would it make any sense to supply a BP garage in Cornwall from the Grangemouth refinery in Scotland? Oil companies have had an agreement in place for decades to supply each other. If anyone's in doubt, just go and stand on the A5117 outside of the loading terminals at Stanlow and watch the different companies roll up to get their fuel . (It's not just petrol either.)There are a number of pipelines around the country and these go to shared terminals, remember that huge explosion and fire a few years ago that was at a BP terminal supplied by a Shell pipeline.
Now then, I can neither confirm or deny that individual oil companies have the ability to add their own "boosters" at the gantries, I've no idea TBH , back in the days when I worked at Stanlow they didn't have that ability.
Pete
I'm at Esso Fawley, theres no Super Unleaded here, our Super comes from Hamble or Avonmouth which ever is offering the best price.