Let me ask this elsewhere because it sounds like he was being a Pr@t.
Well got a reply from a Trafpol seems he could have been wrong. Private land is not covered by the Road Traffic Act. Usually Public liability insurance is only required if You are PAYING for the pleasure of using the land or an organised event is taking place in which case the landowner is responsible.
However if you keep checking this thread you might get a more definitive answer.
http://www.pistonheads.com/gassing/topic.a...=94188&f=10&h=0
The guys to watch for are Tonyrec(already answered), xxplod, Gone and Silverback Mike.