This a quote from (if I remember correctly) from someone in the BSA O.C. forum. I can't imagine why he would say it if untrue.
"I’m a fuel tanker driver and can confirm that the base fuel is the same for all garages, branded and non-branded. The difference is the additive injected at the point of loading. Supermarket fuel generally doesn’t have additive added which is why it is cheaper. Branded fuel usually have a summer additive and a winter additive which have different benefits according to the seasons.
When i was on the petrol the additive system went down and we had a man putting it in manually and if i recall correctly it was 5 litres additive to every 2500 litres fuel.
It was 5 litres additive to every 7000 litres of fuel for BP Ultimate!
Back in 1980, I worked on tankships running coastal.
to Immingham, Milford Haven, Pembroke, Falmouth, Plymouth, Amsterdam etc. Carrying petrol & diesel and we might load at an Esso and deliver to Shell or load at BP and deliver to Esso.
I was told a few times that it was all the same stuff for each company.
We never put the additives in but did put the red dye into diesel, it was amazing how little dye was used, can’t recall exactly but it was something like about a gallon every 100 tons."
Rog.