Must be the cheap stuff. For sure it was a Shell garage I passed, where I used to buy my fuel. When I had eclectic cars. They always run better and had greater mpg when using the high octane stuff, it offset the higher price.
Interesting. BMW suggest that the car I have ordered runs best on Shell V-Power. I’m considering using that for the first 1,200 miles run in period, then using Tesco Momentum Super Unleaded, with every 4th refuel being Shell V-Power. However, the supplying BMW dealer tells me that they use standard unleaded on all their cars, including full fat M cars, but I had read some user reviews on line that they get better performance and mpg from using the more premium fuel, which helps offset the additional cost. That seems to chime with your experience. @kezo I always value your views on these things.