Most Tesco, BP or Shell will do Premium Unleaded (97+). I find that I can always get somewhere that sells it. I usually brim the tank before we leave at the local Tesco, then refill every time it gets to say half, so you know you always have between a half full and completely full tank. If you always have half a tank you can always fine some proper stuff and if you can, you are only mixing it with half a tank of good stuff