18.—(1) The use of force by a person for any of the following purposes, if only such as is reasonable in the circumstances as he or she believes them to be, does not constitute an offence—

(a) to protect himself or herself or a member of the family of that person or another from injury, assault or detention caused by a criminal act; or

(b) to protect himself or herself or (with the authority of that other) another from trespass to the person; or

(c) to protect his or her property from appropriation, destruction or damage caused by a criminal act or from trespass or infringement; or

(d) to protect property belonging to another from appropriation, destruction or damage caused by a criminal act or (with the authority of that other) from trespass or infringement; or

(e) to prevent crime or a breach of the peace.

(2) “use of force” in subsection (1) is defined and extended by section 20.

F9[(3) For the purposes of this section an act is "criminal" notwithstanding that the person doing the act—

(a) if charged with an offence in respect of it, would be acquitted on the ground that—

(i) he or she acted under duress,

(ii) his or her act was involuntary,

(iii) he or she was in a state of intoxication, or

(iv) he or she was insane so as not to be responsible according to law for the act,

or

(b) was a person to whom section 52(1) of the Children Act 2001 applied.]

(4) The references in subsection (1) to protecting a person and property from anything include protecting the person or property from its continuing; and the reference to preventing crime or a breach of the peace shall be similarly construed.

(5) For the purposes of this section the question whether the act against which force is used is of a kind mentioned in any of the paragraphs (a) to (e) of subsection (1) shall be determined according to the circumstances as the person using the force believes them to be.

(6) Notwithstanding subsection (1), a person who believes circumstances to exist which would justify or excuse the use of force under that subsection has no defence if he or she knows that the force is used against a member of the Garda Síochána acting in the course of the member's duty or a person so assisting such member, unless he or she believes the force to be immediately necessary to prevent harm to himself or herself or another.

(7) The defence provided by this section does not apply to a person who causes conduct or a state of affairs with a view to using force to resist or terminate it:

But the defence may apply although the occasion for the use of force arises only because the person does something he or she may lawfully do, knowing that such an occasion will arise.

(8) Property shall be treated for the purposes of subsection (1) (c) and (d) as belonging to any person—

(a) having the custody or control of it;

(b) having in it any proprietary right or interest (not being an equitable interest arising only from an agreement to transfer or grant an interest); or

(c) having a charge on it;

and where property is subject to a trust, the persons to whom it belongs shall be treated as including any person having a right to enforce the trust.

Property of a corporation sole shall be treated for the purposes of the aforesaid provisions as belonging to the corporation notwithstanding a vacancy in the corporation.

F10[(9) In subsection (3) "intoxication" means being under the intoxicating influence of any alcoholic drink, drug, solvent or any other substance or combination of substances.]