Crimes Against Humanity and War Crimes Act 2000
14. (1) In proceedings for an offence under any of sections 4 to, 7, it is not a defence that the accused was ordered by a government or a superior — whether military or civilian — to perform the act or omission that forms the subject-matter of the offence, unless
(a) the accused was under a legal obligation to obey orders of the government or superior;
(b) the accused did not know that the order was unlawful; and
(c) the order was not manifestly unlawful.
(2) For the purpose of paragraph (1)(c), orders to commit genocide or crimes against humanity are manifestly unlawful.
Superior orders
Manifestly unlawful order
EDIT.