Gundoc, I'm sure that the law protects the landowner. The people I met hiking were all well-behaved (the louts were in the pubs). I saw very little evidence of littering or other damage, and people were quick to pick up anything accidentally dropped by others. They were also very mindful of the owner's rights and requests.
From what I have seen in the US, I don't think such a law would be workable. There are too many people here who show their appreciation for public access by trashing the place.