(1) Where any person is trespassing or has trespassed on any place, an occupier of that place may, at the time of the trespass or within a reasonable time thereafter, warn him to stay off that place.
(4) Subject to subsection (5), every person commits an offence against this Act who, being a person who has been warned under this section to stay off any place, wilfully trespasses on that place within 2 years after the giving of the warning.