A disclaimer would verify that they know the place is dangerous. A disclaimer does not disclaim them from a duty of care, since they have noted it is dangerous (by asking for a disclaimer) they could be held accountable as they grant access.
By putting procedures in place, they must now ensure the place is safe, which of course they cant do.
The best thing they could do is put up a "Danger keep out" sign and turn a blind eye to people accessing the site.
The law is a bit of a mine field, disclaimers are very rarely enforceable in this country.
Exploring the mines of Cornwall and making some bloody good mates on the way!