Hi Paul, you may be surprise, but the best fuel is Tesco 99, a couple of Atom owners had tried it, and they confirmed it was noticebly better than shell or bp...
http://www.pistonheads.com/gassing/topic.asp?h=0&t=302977&hw=+%2Btesco+%2B99
I agree with Lorne and Simon, if you wanted to take full advantage of hi octane fuel, you would really need to have your ecu re-mapped....
