Interesting Ricky.
I remember when Autocar did a test with an Astra VXR on the fuels and found the opposite. BP Ultimate actually produced less power than normal unleaded, and V Power came out on top. Tesco 99 was marginally less than V Power IIRC.
I know that I notice the difference in mine, I used to use BP Ultimate, and apart from the horrendous price of the stuff, the fuel consumption was down to about 22mpg. With V Power it's between 25-26mpg and goes a lot better.
I haven't tried Tesco 99 so can't comment.