So you carry on using Tesco and I will use Shell. Not much cheaper locally to justify driving out of my way because apparently Tesco is the best fuel, as you want me to believe.
My experience with shell or BP, even their regular fuels, they're better than the regular from Sainsbury's, Morrisons and Tesco. Never tried Asda. Premium fuel, just tried shell and BP. Shell returned better mpg for me. Will try BP as my partner Mercedes runs better on BP, but mine is fine ATM with shell, so any improvement from my 60+mpg is a given.
Even worst someone spend 30k plus for a car and be worried at 2 pence per litre difference. Now you'll tell me to don't waste 2 pounds in screenwash and use plain water, as works, until the pump clogs and those 2 pounds every few months will sound like a bargain.
And the only reason I would consider Tesco's fuel would be if going for their nastiest fuel. No point paying premium over Tesco's fuel. As I wouldn't pay premium for a Primark t-shirt,but have no problems paying what they're worth.