General defences

CRL.09 — General Defences

General defences negate liability where the prosecution has otherwise proved actus reus and mens rea. Distinguish complete defences (acquittal) from partial defences (loss of control, diminished responsibility — murder only, reducing to manslaughter; covered separately).

Self-defence / defence of another / property (complete)

Governed by the common law plus s.76 Criminal Justice and Immigration Act 2008 (and s.3 Criminal Law Act 1967 for crime prevention). Two limbs:

• Necessity (subjective): Was force necessary on the facts as D believed them to be? A genuine but mistaken belief works — even if unreasonable — unless the mistake is due to voluntary intoxication (O'Grady; s.76(5)).
• Proportionality (objective): Was the degree of force reasonable in those circumstances? Householder cases (s.76(5A)): force is unlawful only if grossly disproportionate (R v Ray). D need not wait to be struck; no duty to retreat (s.76(6A)).

Duress by threats (complete; NOT to murder/attempted murder/treason)

Two-stage Graham/Hasan test: (1) subjective — D reasonably believed in a threat of death or serious injury to self/family/those D is responsible for; (2) objective — a sober person of reasonable firmness sharing D's relevant characteristics would have given in. Threat must be imminent, no safe avenue of escape, and crime nominated. Bars (Hasan): voluntary association with violent criminals where coercion was foreseeable.

Duress of circumstances / necessity

Same two-stage test, threat arising from circumstances rather than a person (Pommell, Martin). True necessity is narrow (Re A).

Intoxication (a denial of MR, not a true "defence")

• Voluntary intoxication: a defence only to specific intent crimes (e.g. murder, s.18) if D lacked MR (DPP v Majewski). No defence to basic intent crimes (assault, manslaughter, s.20) — recklessness is supplied by getting drunk. "Drunken intent is still intent" (Sheehan).
• Involuntary (spiked, prescribed): defence if it negated MR (Kingston — a drunken intent still convicts).
• Dutch courage: no defence (Gallagher).

Insanity & automatism

• Insanity (M'Naghten): defect of reason from disease of the mind → D didn't know the nature/quality of the act, or that it was wrong (legally — Windle/Keal). Verdict: not guilty by reason of insanity. D bears the legal burden (balance of probabilities).
• Automatism: total loss of voluntary control from an external cause (sane automatism → acquittal). Internal cause = insanity. Self-induced automatism may bar the defence.

Common traps

• Mistaken self-defence belief from voluntary intoxication = no defence (s.76(5)).
• Duress is never available to murder (Howe) or attempted murder (Gotts).
• "Grossly disproportionate" applies only to householders, not all self-defence.
• Insanity reverses the burden onto D; most other defences D need only raise, then prosecution disproves.