Wouldn't risk it with petrols, and most modern diesels. Old school derv's yeah no problem, did our Maestro diesel after spilt oil everywhere after a service, d'oh! Jet washed it all out and it came up spanking! Used to do the 600 too as all the ecu gubbins was inside the cabin
http://www.autoglym.com/enGB/product...6VQ=FG&Range=1
Some of this ^ should do the trick, but instead of washing off with hose use like Tim said, damp cloth with plenty of water in a bucket etc.. to rinse the cloth clean