I bash in London at Burgess Park track they run every other sunday, nice short track and lovely bunch of guys.
[link=http://www.burgessnitro.co.uk/index.htm]Burgess Nitro[/link]
You could also try Dartford race track, not been there but looks like a good track.
[link=http://www.dartfordracetrack.com/]Dartford Race Track[/link]