Criminal Law Defences and Lines of Defence

Criminal Law 2025 - Defences and Lines of Defence

Introduction

• A defendant is acquitted if the prosecution fails to prove beyond a reasonable doubt that the defendant is responsible for the actus reus and had the applicable mens rea. Guilt requires the absence of any relevant defence.
• This area involves complex language and considerations regarding burdens and standards of proof.

Defences vs. Lines of Defence

• Line of Defence: An argument for acquittal based on the prosecution's failure to prove the elements of the offense to the required standard. Example: Intoxication or mental impairment preventing proof of subjective mens rea beyond a reasonable doubt.
• Defence: An argument accepting conduct and fault elements but asserting a valid defence applies. Example: Self-defence, where the defendant admits to assault but claims it was justified; lack of fault in strict liability, where the defendant argues the actus reus occurred without their negligence.

Offences may include express exceptions. For example, s7 of the Misuse of Drugs Act 1975, which makes possessing/using drugs an offence, is subject to:

• s8 (providing an exception)
• a license
• s7(3) sets a specific defence; and
• s7(4) preserves any other applicable defence.

Some offences are defined as conduct "without a lawful excuse" or "lawful authority" (e.g., s202A Crimes Act).

Implied Exceptions

• The defence may argue implied exceptions. Example: Conduct considered disorderly should not be if it’s a valid exercise of freedom of expression.

Defence or Element?

• Sometimes, unclear if something is a defence or an element (e.g., consent in assaults).
• Sexual violation includes the absence of consent as an element in the statute.
• Assaults (including indecent assaults) have no such language, yet lack of consent is core.

Defences/Lines of Defence and Burdens/Standards of Proof

The burden of proof may fall on the defendant or prosecution, depending on statutory construction.

• Language such as "until the contrary is proved" or "unless the defendant shows" typically places a legal burden on the defendant, requiring proof on the balance of probabilities.
• Otherwise, the prosecution must prove guilt, including that exculpatory circumstances do not apply beyond a reasonable doubt (Woolmington principle).
• The defendant may have an evidential burden to raise the issue.

Examples:

• Evidential burden on defendant: self-defence (s48), duress of circumstances (common law), compulsion (s24).
• Legal burden on defendant: insanity (s23), suicide pact (s180(4)), money laundering for legal purpose (s244). Arises in multiple statutes such as s65AA Civil Aviation Act 1990 and s105(7) Fisheries Act 1996.

Exceptions

• s67(8) Summary Proceedings Act 1957 formerly required the defendant to prove any exception, etc., in summary proceedings, but this has been removed.
• Schedule 3 Criminal Procedure Act 2011 now includes express provisions for when a defendant must prove an exception.
• King v Police [2016] NZHC 977 clarified that if there’s no express requirement for the defendant to prove the exception, there’s just an evidential burden.

Purposive Arguments

• For offences criminalizing conduct without a license, the defendant can often prove the existence of a license more easily than the prosecution can disprove it.

If the prosecution must prove the absence of a defence, this can be incorporated into the offence analysis. Using male assaults female (s194 CA) and self-defence:

Actus Reus

• Conduct Involved – Assault
• Circumstances – (i) Gender of victim and assailant; (ii) Absence of self-defence
• Consequence – N/A

Mens Rea/Fault Element

• Fault Element as to Conduct – Intention
• Fault Element as to Circumstances – Knowledge as to gender of victim
• Fault Element as to Consequence – N/A
• Ulterior Fault Element – N/A

A mistake of fact regarding gender would preclude liability.

Categorisations of Defences

Defences can be classified in several ways:

Justifications and Excuses

• Justification: Makes conduct lawful. (actus non reus)
• Excuse: Unlawful, but not requiring criminalisation.
• Statutory defenses are determined by whether the action is "justified" or "protected from criminal responsibility".
• Common law defences are considered individually.
• Both justifications and excuses result in verdicts of Not Guilty, but they differ in relation to civil liability.

Actus Reus and/or Voluntariness, or Mens Rea Defences

A defence may relate to actus reus, mens rea, or both.

• Actus reus defence: Self-defence means an assault isn't an unlawful application of force.
• Mens rea defence: Doli incapax presumption (s22 CA) rests on a lack of awareness of wrongfulness, i.e., of moral fault; infancy (s21) – conclusive lack of awareness.
• Both: Insanity (includes mens rea - not knowing nature or quality of act or that morally wrong) but has been interpreted to include situations of automatism.
• Mistake of fact usually negates fault (mens rea) but may combine with conduct to make the latter lawful.

The effect on actus reus is important for participation by others. If the principal has self-defence, there is no actus reus for any secondary party.

General and Specific Defences

• General: Apply to all offences.
• Specific: Apply to a particular offense or range of offences.

Statutory and Codified Defences, Common Law Defences

• Section 20 Crimes Act preserves common law justifications or excuses if not otherwise codified.
• Duress by personal threat is codified as compulsion (s24), but duress by circumstances is a common law matter.

Complete and Partial Defences

• Partial defences: Reduce an offence from a more to a less serious one (e.g., suicide pact (murder to manslaughter), infanticide).
• A line of defence may argue for a lesser mens rea, leading to a lesser offence.

Intoxication

• Intoxication may be an element (e.g., driving offences), a line of defence, or a mitigation (though precluded now by s9(3) Sentencing Act 2002).

Intoxication and Voluntariness

• Extreme intoxication may produce a lack of voluntariness (automatism).
• A drunken decision is sufficient; lack of volition is required.
• Failure to remember due to intoxication is not the same as lacking volition.
• Deciding to become inebriated for courage provides the necessary volition.

Intoxication and Mens Rea

• A drunken mens rea is enough.
• Lack of memory is not the same as lacking mens rea.
• Taking Dutch courage may be relevant to whether the mens rea is made out.

English Approach

• Getting drunk is sufficient mens rea for some crimes (DPP v Majewski [1977] AC 443).
• This applies to crimes of basic intent (intention as to conduct or recklessness) but not to crimes of specific intent (intention as to consequence or ulterior intent).

On element analysis:

Actus Reus

• Conduct Involved –

• Circumstances –

• Consequence –
  Mens Rea/Fault Element

• Fault Element as to Conduct – Intention or Intoxication

• Fault Element as to Circumstances – Knowledge despite intoxication

• Fault Element as to Consequence – Intention despite intoxication

• Ulterior Fault Element – Intention despite intoxication

New Zealand and Australian Approach

• In R v Kamipeli [1975] 2 NZLR 610, the Court of Appeal held that drunken intent is sufficient, but the prosecution must prove intent wherever it is a mens rea (or recklessness), and intoxication does not justify an exception to this rule.
• Australian courts have declined to follow Majewski (O’Connor (1979-80) 146 CLR 94).

Intoxication and Strict/Absolute Liability

• Absolute liability: Only the commission of actus reus matters (unless a positive defence applies). Intoxication is only relevant if it produces involuntariness.
• Strict liability: The issue is whether alcohol prevents the defendant from proving a lack of fault.

Involuntary Intoxication

• In New Zealand, the only question is the effect of intoxication.
• In England, the rule that intoxication is a mens rea for basic intent crimes applies only to involuntary intoxication (R v Kingston [1995] 2 AC 355).

Mistake

Introduction

• The defendant's perception may differ from objective reality.
• Mistakes may be of fact or law.

Examples:

• Factual: Taking the wrong luggage, believing a person has a weapon when it’s a phone.
• Law: "Finders keepers", believing cannabis is legal.

Generally, ignorance of the law is no defence (s25 Crimes Act), but a claim of right can be based on a mistake of law. Criminal liability usually depends on the defendant’s perceptions, but there sometimes needs to be an objective justification.

Mistake of Fact – Elements of Offence and Justifications

• Self-defence involves looking at the circumstances the defendant perceives (s48), but the amount of force used is judged objectively.
• "Dishonestly" depends on the subjective belief of the defendant as to consent or authority (s217).

The doctrine of concurrence gives rise to a "defence" of mistake of fact.

Initial Version

• R v Tolson (1889) 23 QBD 168 established that an honest and reasonable belief in circumstances that would make the act innocent is a good defence.
• Similarly, belief as to justification for self-defence at common law had to be honest and reasonable.

Updated Version

• DPP v Morgan [1976] AC 182 determined that an honest mistaken belief in consent precluded mens rea for rape, but the unreasonableness of belief was evidential matter.
• Similar change in relation to defences: R v Beckford [1988] AC 130 (PC) - belief not reasonable belief.

In NZ:

• The first question is what the statute provides. For example, s48 defense turns on belief, s55 re defence of dwelling house requires reasonable and probable grounds.
• Sexual violation requires belief in consent on reasonable grounds (s128), whereas dishonesty is subjective.
• In Millar v MOT [1986] 1 NZLR 660, the court endorsed the general proposition that an honest belief in a state of affairs or as to the existence of a fact, which if true would make the act innocent, will provide a defence itself.

Examples

• R v Nazif [1987] 2 NZLR 122 - honest belief of consent is defence to indecent assault.
• R v Wood [1982] 2 NZLR 233, honest belief cannabis seeds were tomato seeds – defence not require reasonable grounds.

Reasonableness is an evidential matter, going to whether the court accepts that the belief is honestly held.

Mistake will also work in relation to the subjective aspect of recklessness.

Summary

In relation to the actus reus and subjective mens rea states, an honest mistake provides a defence, subject to a contrary statutory provision.

Mistakes and Excuses

More likely to have objective element at common law. For example, duress of circumstances requires reasonable grounds. However, if the statutory excuse defence, it may have subjective language, such as compulsion (S24)

Mistakes and Negligence, Strict Liability or Absolute Liability

• Objective fault elements - whether mistake objectively reasonable.
• Similarly, absence of fault defence to strict liability needs to consider whether any mistake is reasonable.
• For absolute liability, MR not relevant: but may be a statutory defence.

Mistake of Law

Generally not a defence (s25 Crimes Act). However,

• Claim of right in relation to property offences allows errors of law.
• s22 requires knowledge of being against law for those under 14.
• Law must have been published (Lim Chin Aik v R [1963] AC 160).

Defence of Officially-Induced Error as to Law

Supreme Court of Canada (R v Jorgenson, (1995) 102 CCC (3d) 97; [1995] 4 SCR 55) set 5 criteria:

$(1)$ accused considered the legal consequences

$(2)$ accused sought advice from the appropriate official

$(3)$ the advice was reasonable in the circumstances

$(4)$ advice was erroneous

$(5)$ accused relied on the advice.

Partially recognised in NZ in Tipple v Police [1994] 2 NZLR 78.

Mistakes of Law or Fact?

Not always clear whether a mistake is one of law or fact.

Examples

• R v Metuariki [1986] 1 NZLR 488, CA - mistaken belief that nothing illegal went to the nature of the plant material not to its legal classification, and so it was not a mistake of law.
• Police v Taggart [1973] 1 NZLR 732 - not know active ingredient was an alkaloid of yohimba, a statutory poison; so s25 applied.
• R v Foox [2000] 1 NZLR 641 - “The Crown did not have to establish that Mr Foox knew that airguns were restricted weapons. Mr Foox's ignorance of the law was no excuse.”.
• R v Cave [2011] NZAR 498 - error as to whether road was mistake of law.But
• Booth v MOT [1988] 2 NZLR 217 - But since disqualification runs by law from when judge says, which will be on conviction, why not mistake of law?

R v Cameron [2017] NZSC 89

Supreme court considered in complex setting, here the court held that:

$(i)$ need for MR as to illegality of drugs, and correct MR was recklessness

$(ii)$ if defendant aware of identity of drug, but not aware listed in statute as illegal, that would generally be an error of law

$(iii)$ or controlled drug analogue, knowing identity of drug later found to be substantially similar not sufficient to establish MR, but was evidentially significant

$(iv)$ unlike in Metuariki and Taggart, defendants had turned mind to whether drugs illegal and got advice, but that advice was shown to involve a mistake as to the construction of the statute and so was a mistake of law

Judge’s Approach

$(i)$ if no evidence that lack of knowledge that controlled drug, judge can rely on presumption of mens rea (Strawbridge approach – see Strict Liability),

$(ii)$ if evidential basis for lack of knowledge,

$(a)$ prosecution to prove MR beyond reasonable doubt,

$(b)$ MR exists if knew or believed drug was controlled or analogue, or reckless as to whether it might be controlled or analogue

$(c)$ belief that not analogue because of mistake as to law as to what amounts to analogue not a mistake of law defence.

Summary

Illegality can be through designation or description

Mistakes and Impossibility

If mistaken belief that shooting human wearing possum hat when in fact shooting possum, or belief stealing someone else’s umbrella when own, or belief shooting protected animal when not in law protected – AR not committed inchoate offences (attempts, conspiracy, incitement) and the question of “impossibility” – in essence, an inchoate offence may still be committed.
Responsibility for actus reus requires being in control of own conduct.

Responsibility for Actus Reus

Requires being in control of own conduct. However, involuntariness arising from conditions amounting to insanity has to be proved as insanity, which limits the role for sane involuntariness.

Insanity

Introduction

Mental disorder may give rise to issues of procedure, evidence and substantive law

$(i)$ whether defendant fit to stand trial - see Criminal Procedure (Mentally Impaired Persons) Act 2003

$(ii)$ whether a sentence should take into account mental disorder (or be specifically designed to allow treatment)

$(iii)$ whether or not MR made out

$(iv)$ whether defence of insanity at the time of the offence made out – which not lead to verdict of Not Guilty, but special verdict, formally Not Guilty by Reason of Insanity

Sections 24-26 of CPMIPA allow those acquitted to be detained under mental health or intellectual disability legislation, or released.

M’Naghten Rules

These followed a Victorian moral panic, these include:

$(1)$ What is the law respecting alleged crimes committed by persons afflicted with insane delusion in respect of one or more particular subjects or persons

$(2)$ What are the proper questions to be submitted to the jury, where a person alleged to be afflicted with insane delusion respecting one or more particular subjects or persons, is charged with the commission of a crime (murder, for example), and insanity is set up as a defence

$(3)$“… the jurors ought to be told in all cases that every man is to be presumed to be sane, and to possess a sufficient degree of reason to be responsible for his crimes, until the contrary be proved to their satisfaction; and that to establish a defence on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong."

$(4)$ the answer must of course depend on the nature of the delusion: but, making the same assumption as we did before, namely, that he labours under such partial delusion only, and is not in other respects insane, we think he must be considered in the same situation as to responsibility as if the facts with respect to which the delusion exists were real."

$(5)$ the medical man, under the circumstances supposed, cannot in strictness be asked his opinion in the terms above stated, because each of those questions involves the determination of the truth of the facts deposed to, which it is for the jury to decide, and the questions are not mere questions upon a matter of science, in which case such evidence is admissible."

The NZ Codification

The relevant codification in New Zealand - s23 CA: contains the following elements:

• Sanity presumed “until the contrary is proved” (so for defence to prove on the balance of probabilities – ie legal burden, not just an evidential burden – though note s20(5) Criminal Procedure (Mentally Impaired Persons) Act 2003 allows judge to leave question of insanity to jury even if defendant has not raised issue, provided evidence of insanity).
• Proving insanity involves showing “natural imbecility or disease of the mind” to the extent that incapable either of understanding the nature and quality of the act or omission or of knowing that morally wrong having regard to commonly accepted standards of right and wrong.
• Insanity before or after actions, or partial delusions, may be evidence that had “condition of mind” so as to be “irresponsible”.
• Other people can be convicted – so not make act lawful.

Differences from M’Naghten Rules

requirement for “defect of reason” caused by disease of mind removed: but the defect of reason is merely the link between the disorder/disease of the mind and the consequence of it

• adds “natural imbecility” – though this will probably lead to unfit to stand trial
• refers to capacity to have known nature/quality or wrongness rather than not knowing – but in R v MacMillan [1966] NZLR 616 at 621, Court of Appeal held s23 should be construed to mean “did not know”.
• reference to moral wrongness

State of Mind Elements of Insanity

“Nature and quality of the act” refers to physical attributes of act.

“Morally wrong” – makes it plain that it covers situation where defendant knew against law (which was the import of M’Naghten – though that had been rejected in Australasian cases) but did not know that act morally wrong.

“having regard to the commonly accepted standards of right and wrong” – in R v Macmillan [1966] NZLR 616 (CA) prosecution suggested it meant knowledge of moral wrongness in eyes of others; rejected because it would exclude, eg, those whose illness involved a private code of morality – who might know that others had a different view, but would reject it because of their illness.

“Disease of Mind”

Tully [2020] NZCA 690, [132]-[133] - whether something is a disease of the mind is a legal question for the judge (noting also s20(4) of CP(MIP)A); on facts, delusional disorder about skin and traits consistent with a narcissistic personality disorder not enough.

Examples showing how broad concept is (and how it extends beyond mental disorders)

• Kemp [1957] 1 QB 399: arteriosclerosis (hardening of the arteries) – because it has an effect on the brain, it is a disease of the mind in just the same way as psychotic illnesses such as schizophrenia
• Bratty v AG [1963] AC 386: epilepsy is a disease of the mind
• Police v Bannin [1991] 2 NZLR 237: Fisher J held that accused with Kleine-Levin syndrome – ie periodic episodes of prolonged sleep followed by several days of impaired consciousness and inappropriate behaviour – was a disease of the mind and so any automatism would be insanity

Voluntariness

Basic Idea

Criminal liability – based on choice to offend – so needs to be voluntary; lack of deliberative control means not criminal; similarly, reflex actions.

Example - Hill v Baxter [1958] 1 QB 277: dangerous driving charge – court notes that acquittal could follow if driver out of control because of events such as a sudden illness, a stroke, an epileptic fit, being hit by a stone or attacked by a swarm of bees.
The need for voluntariness comes before any question of mens rea and so applies even if there is no mens rea, ie in strict and absolute liability situations, because it is a part of the question of responsibility for the actus reus: see Kilbride v Lake [1962] NZLR 590 (where an offence of failing to display a warrant of fitness was held not made out where the warrant had been stolen).

However, note that antecedent fault may preclude this line of defence: eg Ryan v R (1967) 121 CLR 205 – involuntary or reflex squeezing of trigger, but that was a probable consequence of carrying out armed robbery, so not involuntary as a matter of law.

Cameron v R [2021] NZCA 80, at para [59], the Court of Appeal noted that there is no presumption of voluntariness, but that there is an evidential burden on the defendant to raise mental incapacity (which is in the context of a discussion of involuntariness and so equates to that), whereupon the prosecution has to prove voluntariness.

Involuntariness and intoxication

See intoxication above: it has to be an extreme situation.

Defences and voluntariness

Consider also the defences of self-defence, compulsion and necessity: these also focus on the issue of whether the freedom of choice was taken away from the defendant. However, they are not examples of lack of voluntariness because they apply when the defendant in fact acted voluntarily and with the necessary mens rea, but is justified or excused because the choice made was not one meriting criminal condemnation.

Involuntariness in the form of automatism – overlap with insanity

Automatism is another instance of a lack of voluntariness, essentially where normal control over body lost - so no deliberative control.

In Police v Bannin [1991] 2 NZLR 237, held that partial awareness of what doing not amount to automatism (though was relevant to whether formed mens rea: did in relation to assault but not in relation to the “intent to commit a crime” element of burglary.

Important case of Cottle [1958] NZLR 999 – defendant consumed lots of alcohol, arrested breaking into warehouse: defendant claimed acting in automatic state, and there was evidence he might have had an epileptic fit induced by alcohol. CA – some automatism consistent with sanity, in which case defendant has to raise it and then prosecution’s overall burden of proving guilt kicks in; but if automatism arises from something capable of being a disease of the mind, rules relating to insanity apply.

In contrast, a failure to take insulin, leading to a hyperglycaemic coma, is a disease of the mind because it is internally caused: see R v Hennessey [1989] 1 WLR 287.

Absence of evidence of external cause means must be something within the wide understanding of a disease of the mind

• Rabey v R [1980] 2 SCR 513: dissociative state arising from infatuation and stress – amounted to an internally-caused malfunctioning of the mind as there was no transient external cause that could explain the actions.
• R v Yesler [2007] 1 NZLR 240: stresses and disappointments felt were normal and so could not give rise to a dissociative state in the absence of a disease of the mind that was likely to recur – so only insane automatism was possible.

Note automatism and strict liability

in Keech v Pratt [1994] 1 NZLR 65 – person found driving after suffering a concussion (and factual finding that acting as automaton) – charged with driving with excess alcohol – held that strict liability offence, though subject to defence of total absence of fault, and so open to driver to prove automatism. But why is it not for prosecution to prove its absence if it is not insane automatism?

Sleepwalking

Supreme Court has considered this in Cook v R [2025] NZSC 44 – sexual violation – some evidence that had a parasomnia (which includes sleepwalking and sleeptalking) called sexsomnia (sexual touching whilst asleep – recognised condition with diagnostic criteria); another doctor excluded the condition because defendant had also used alcohol and pain-killers.

Supreme Court:

$(i)$ disease of the mind – legal not medical concept, not to be given narrow meaning and not depend on it being a mental illness; requires proof to civil standard of disease or disorder affect reason, memory or understanding so that unable understand nature/quality or moral error

$(ii)$ Cameron essential correct – sexsomnia was a disease of the mind.

Intoxication and Insanity

See R v Dixon [2008] 2 NZLR 617: Court of Appeal noted that disease of the mind requires more than a merely transitory state caused by intoxicants([38]-[39]: but note that extreme intoxication is capable of producing psychotic effects – would that take it outside the area of being merely transitory?); but noted that intoxicants can trigger latent mental illness ([39]-[40]); and also that intoxication can have the result that under s23(2)(b) the defendant does not have the awareness of moral wrongness ([42]).

Duress/Compulsion/Necessity

Note need for choice: so what if choice constrained and so not free? In short, deliberate action (so not automatism) and mens rea: but does the constrained choice provide a defence (and if so justification or excuse) or just mitigation; and how far does law go – eg, poverty and theft?

Common law

Common law developed defence of necessity (in relation to which various words are used interchangeably), part of which split over time into self-defence (assault to prevent assault of self or another) and part of which carried on as necessity (arising from threats from another person or from circumstances).

Martin [1989] 1 All ER 652: driving whilst disqualified, taking son to work when he had overslept and wife obsessively fearful that he would lose his job and the husband thought she would commit suicide if he did not act – Court of Appeal held that defence should have been left to jury.

The elements required were: objectively reasonable and proportionate action to avoid the threat of death or serious injury – which entailed that the defendant was impelled to act because of his reasonable belief as to the situation giving good cause to fear death or serious injury if he did not act, and that a sober person of reasonable firmness with the accused’s characteristics would have so acted.

Bowen [1996] 4 All ER 837 - characteristics to be taken into account – age and gender, recognised psychiatric conditions, serious physical disabilities (on the basis that they might inhibit self-protection), and pregnancy.

R v Hasan [2005] 2 AC 467 - threats of violence from others also covered, including threats to close family and friends; reasonable belief in threat being carried out central – so key to defence is lack of reasonable alternative.

Necessity summarised by Canadian Supreme Court in Perka v R (1984) 13 DLR (4th) 1, 14 CCC (3d) 385 (SCC): need (a) situation of urgency and imminent peril; (b) compliance with law “demonstrably impossible”, ie, no reasonable legal alternative to committing offence; and (c) harm done by defendant proportionate to harm sought to be avoided. Necessity not available for murder, or secondary party, or attempted murder, also excluded for treason.

Available for all other offences: see Abdul-Hussain [1999] Crim LR 570 – should have been left open on a charge of hijacking a plane.

New Zealand

Self-defence – codified in s48 as a justification, with subjective perception of threat and reasonableness of force in light of perceived threat.

Necessity split into two – compulsion (necessity through threats) under s24 and duress of circumstances as a common law defence under s20.

Compulsion in NZ

Section 24 CA codifies that part of the defence which is based on threats of violence. It requires:

• threats of death or grievous bodily harm if crime not committed (so not applicable for lesser threat)
• immediacy (on which see Maurirere [2001] NZAR 431
• presence of person making threats at time of offence
• belief that threat will be carried out (ie a standover situation); the belief has to be genuinely held: reasonableness goes to the evidence of genuineness (see Raroa [1987] 2 NZLR 486); this is a modification of the common law
• not available if person being threatened is a party to any association or conspiracy involving compulsion.
• not available for list of serious offences set out in s24(2),

Simester and Brookbanks make the point at p550 (of their 5th ed) that s24 does not expressly limit the defence to threats to the person who commits the offence: but that would be more consistent with the strict construction of the language and the need for a “standover” situation.
Note also that the opportunity to escape or seek protection is relevant to whether or not the defendant was acting under compulsion.

Duress of Circumstances

Note that section 44 of the Search and Surveillance Act 2012 indicates that Part 2 of the Act (which covers various powers of search) does not affect the “common law defence of necessity as it applies to persons who are not constables”. This seems to recognise the defence.

Comparison between Necessity and Self-Defence

Compulsion/duress of circumstances provide an excuse rather than a justification - ie an excuse for what would otherwise be criminally punishable without declaring that the actus reus is in fact lawful.

Self-defence is a justification.

Statutory Necessity Defences

Note that there may also be specific statutory defences of necessity – see, eg, s154N Biosecurity Act 1993: this sets out various offences , sets out the elements of the lack of fault/due diligence (s154N(3)) and also indicates that there is a further defence of “necessity” that covers life/health/serious property damage/resources.

Further Consideration of Some Specific Defences

The full details of some defences/lines of defence are considered further in the context of the detailed consideration of specific offences.

In short:

• Consent – absence of consent is an element of some sexual offences and in relation to assaults there is a lack of clarity as to whether it is a defence or its absence is an element.
• Self-defence – this is a defence to assault offences (potentially up to homicide – where its application in relation to defendants who have been the victims of domestic violence is problematic); it means that the actus is not reus.
• Other lawful uses of force – eg arrest, defence of property, discipline: these are invariably defences to assault and so considered in that context.