Go-Karts?

[Wharn]

After a lengthy Mario Kart tournament, one of my friends suggested that we ought to go for a real Go-Kart outing someday. Personally I think it's a good idea (haven't been in years), but I don't know of any decent tracks in London. Has anyone here ever been go-karting in the Forest City before? If so, do you know anywhere closeby (ie within 20 minutes of the built-up area) that has a moderately challenging track? We're not talking stig-level, but something beyond kiddy karts would be nice.