Agree about Supermarket petrol, a local taxi firm stopped their drivers using it as it was burning out valves, as there are very little or no additives in the cheap fuel which help mileage and look after the engine. It just meets the legal spec and that's it. We always stick to BP, Shell or Texaco, the BP station is just 100yds away.
They started another station a couple of miles away on the A10 near us that started selling the cheap stuff at 4p to 5p under the BP price, pretty cheap but not for my Jazz. You get what you pay for in this life, most of the time.