1047 (b) the person could not reasonably be expected to guard against the bringing about of that physical element. Duress 40.—(1) A person is not criminally responsible for an offence if he or she carries out the conduct constituting the offence under duress. (2) A person carries out conduct under duress if and only if he or she reasonably believes that (a) (b) (c) a threat to cause death or serious harm has been made that will be carried out unless an offence is committed; and there is no reasonable way that the threat can be rendered ineffective; and the conduct is a reasonable response to the threat. (3) This section does not apply if the threat is made by or on behalf of a person with whom the person under duress is voluntarily associating for the purpose of carrying out conduct of the kind actually carried out. Sudden or extraordinary emergency 41.—(1) A person is not criminally responsible for an offence if he or she carries out the conduct constituting the offence in response to circumstances of sudden or extraordinary emergency. (2) This section applies if and only if the person carrying out the conduct reasonably believes that— (a) (b) (c) circumstances of sudden or extraordinary emergency exist; and committing the offence is the only reasonable way to deal with the emergency; and the conduct is a reasonable response to the emergency. Self defence 42.—(1) A person is not criminally responsible for an offence if he or she carries out the conduct constituting the offence in self defence. (2) A person carries out conduct in self defence if and only if he or she believes the conduct is necessary: (a) (b) (c) (d) (e) to defend himself or herself or another person; or to prevent or terminate the unlawful imprisonment of himself or herself or another person; or to protect property from unlawful appropriation, destruction, damage or interference; or to prevent criminal trespass to any land or premises; or to remove from any land or premises a person who is committing criminal trespass— and the conduct is a reasonable response in the circumstances as he or she perceives them. (3) This section does not apply if the person uses force that involves the intentional infliction of death or grievous harm— (a) to protect property; or (b) to prevent criminal trespass; or (c) to remove a person who is committing criminal trespass. (4) This section does not apply if— (a) (b) the person is responding to lawful conduct; and he or she knew that the conduct was lawful. (5) For the purposes of sub-section (4) conduct is not lawful merely because the person carrying it out is not criminally responsible for it. Lawful authority 43. A person is not criminally responsible for an offence if the conduct constituting the offence is justified or excused by or under a law.