There is a model club near (Elmbridge Model Club) me that has been threatening to start a car section for a while (they are mainly boats and planes). I don't know too much about the club but know they have quite a lot of land and are within spitting distance of the M25 by the Windsor/Staines turn off. Might be worth having a word with them?
http://website.lineone.net/~elmbridgemc/