would like to point something out that may not be true to everywhere in the uk.
where i live near aberdeen, my dad is in middle managment at the harbour. I have been at the harbour before. there are maybe 20 or so of these huge silos that contain the same oil, the same petrol, the same diesel. At 9pm a shell truck will come and fill itsself with "shell petrol / desiel" then maybe 20 mins later a BP will come, fill itself from the same tank. Tesco truck- same fuel same for asda, and all those other places. so for people in the aberdeen area, you are being conned if you go to a BP store for 95p / gallon (litres maybe, dont pay attention lol) where you can go to tesco and get it for 87p / litre