(3) This
section does not prevent a person from moving, damaging or destroying a
historic shipwreck situated in any land in accordance with an
excavation permit in force in respect of that land.
(4) It is a defence to
proceedings for an offence under this section if the defendant establishes
that the act giving rise to the offence was done for the purpose of--
(a)
saving human life, or
(b) securing the safety of a ship where the ship was
endangered by stress of weather or by navigational hazards, or
(c) dealing
with an emergency involving a serious threat to the environment.
