There's a new park in Northfleet - Kent (near Gravesend). It only opened 2 weeks ago so i don't know how busy it'll get but there's some nice patches of grass; one huge patch where cows are (or will be) but i doubt you'll be allowed on there, not that that'd stop me.

Great for static flying, ok for buggying i think. I'm going there tomorrow to find out.

Peter