In reply to tombeasley:
Jumping into this one a bit late I know but this may/may not be useful. I suspect anyone dealing with land access issues knows about it anyway but here goes...
As an insurance underwriter who gets involved with land issues a lot I've occasionally given advice to land owners concerned about climbing or similar activities on their land, that there is a common law defense against action being taken called "volenti non fit injuria". Essentially this means "to willing person no harm is done", and is used to mean that anyone taking part in an activity they know to be hazardous, of their own free will, cannot take action against another party (ie land owner) if they suffer injury whilst doing it.
Frustratingly this principle has been less rigidly enforced by the courts over recent years, but for our purposes is a very useful tool if negotiating access as climbers, as we're generally very aware of the risks we undertake. It's a Google-able term to so land owners can even go and check it out for themselves.