Where are the lawyers when you need them?!
My readings in the past have suggested that the law of trespass applies to being on foot, horseback, vehicle or aircraft - needs no bit of ANO or ROTA, therefore.
Dunno about insurance for power planes, but emergency landings without PPR in gliders are covered by our insurance OK.
Once an aircraft has landed, the landowner can get quite sniffy - but if e.g. he/she says you can't take the aircraft/glider away again, it puts him/her into a position of having to look after it adequately, AIUI. All a bit messy if good relations are not preserved.
So my take (and most glider [pilots) is not to casually land on private property without PPR unless forced to, but then apologise, seek a reasonable way out (almost always OK in my experience) and pay compensation if asked for any damage. I once paid towards the local church restoration fund, as requested, even though there was no damage to the field - not worth leaving an upset farmer.
Anyone who just lands regardless of the normal courtesies is going to do much harm to the GA community reputation, IMHO.
Chris N.