I've been running on Vpower since my tuning at PAW and have been getting 23 - 23.5 mpg as an average (still driving it hard).
Anyway, wanted to fill up last week and the garage was out of Vpower

Finished the tank today, still driving hard, and did exactly the same route everyday on both tanks. The Tesco 99 gave me just over 25 mpg

Before asked, my calcs are right. It's always taken from a full tank, miles noted on refill and calculated from the fuel taken to put it back to a full tank. For example; 212 miles / 38.23 L * 4.52 (convert to gallons) is my calculation from this morning and I always work it out this way.