Criminal Defences (Self-Defence, Duress, Insanity & More)
The general defences in English criminal law: self-defence, duress, necessity, intoxication, insanity, diminished responsibility, automatism, loss of control, and consent — when they apply, the evidential burden, and how the prosecution rebuts them.
简介
English criminal law recognises a structured catalogue of general defences that, if successful, either negate an element of the offence (failure-of-proof defences like accident or mistake), provide a justification (self-defence under common law and Criminal Justice and Immigration Act 2008 s.76), or excuse the defendant on the basis of capacity or compulsion (duress, necessity, insanity, automatism, diminished responsibility, loss of control). Each defence has its own evidential burden — once the defence raises 'sufficient evidence', the legal burden shifts to the prosecution to disprove the defence beyond reasonable doubt (R v Lobell [1957] 1 QB 547). The two exceptions are insanity and diminished responsibility, where the defendant carries the legal burden on the balance of probabilities. This topic walks through the modern law on each defence, its statutory and case-law boundaries, and where it intersects with sentencing.
In Brief
English criminal defences fall into three families: failure-of-proof (e.g. mistake), justifications (self-defence, prevention of crime under s.76 CJIA 2008), and excuses (duress, necessity, insanity, diminished responsibility, loss of control, automatism, intoxication). For most defences the defendant only needs to raise 'sufficient evidence'; the prosecution must then disprove beyond reasonable doubt. Insanity and diminished responsibility are exceptions — defendant proves on balance of probabilities.
核心原则
Self-defence — codified by s.76 Criminal Justice and Immigration Act 2008. Test is necessity (subjective) + reasonableness of force (objective). Householders enjoy a wider latitude under s.76(5A) — force must not be 'grossly disproportionate'.
Duress by threats — Hasan [2005] UKHL 22: threat of death/serious injury, reasonable belief, no safe avenue of escape, no voluntary association with criminal gang. Not available for murder or attempted murder.
Duress of circumstances — Martin (1989) 88 Cr App R 343, Pommell [1995] 2 Cr App R 607: applies where circumstances (not threats) coerce. Same Hasan-style criteria.
Necessity — narrow common-law defence. Re A (Conjoined Twins) [2001] Fam 147 — the modern leading authority.
Insanity — M'Naghten Rules (1843): defect of reason from disease of the mind; defendant didn't know nature/quality of act OR didn't know it was wrong. Burden on defendant on balance of probabilities. Special verdict + disposal under Criminal Procedure (Insanity and Unfitness to Plead) Act 1991.
Diminished responsibility (murder only) — Homicide Act 1957 s.2, as amended by Coroners and Justice Act 2009. Recognised medical condition substantially impairing defendant's ability to understand conduct / form rational judgment / exercise self-control. Reduces murder to manslaughter.
Loss of control (murder only) — Coroners and Justice Act 2009 ss.54-55. Replaced provocation. Qualifying triggers: fear of serious violence; things said/done of an extremely grave character giving justifiable sense of being seriously wronged.
Intoxication — voluntary intoxication: no defence to basic-intent crimes (DPP v Majewski [1977] AC 443); may negate specific intent. Involuntary intoxication can negate mens rea if defendant didn't form the necessary intent.
Automatism — total loss of voluntary control caused by external factor; complete acquittal if not self-induced.
Consent — defence to assault but not generally to GBH or worse (Brown [1994] 1 AC 212), with exceptions for surgery, sport, religious mortification, and tattooing.
关键法规
Criminal Justice and Immigration Act 2008
Homicide Act 1957
Coroners and Justice Act 2009
Criminal Procedure (Insanity and Unfitness to Plead) Act 1991
Criminal Damage Act 1971
重要判例
R v Hasan
[2005] UKHL 22
R v Martin (Anthony)
[2001] EWCA Crim 2245
DPP v Majewski
[1977] AC 443
R v Brown
[1994] 1 AC 212
Re A (Children) (Conjoined Twins)
[2001] Fam 147
R v Clinton, Parker, Evans
[2012] EWCA Crim 2
Frequently Asked Questions
Is self-defence different for householders defending their home?
Yes. Section 76(5A) Criminal Justice and Immigration Act 2008 widens the test for 'householder cases' — force is unreasonable only if 'grossly disproportionate', a higher threshold than ordinary self-defence which requires 'reasonable in the circumstances'. The defendant must believe the intruder is a trespasser and the force must be used to defend self / another / property within a dwelling.
Can duress be a defence to murder?
No. R v Howe [1987] AC 417 and R v Gotts [1992] 2 AC 412 confirm duress is not available for murder or attempted murder, even where the defendant was forced to kill at gunpoint themselves. The defence is also unavailable to people who voluntarily associate with criminal gangs and could foresee being put in such a position (Hasan).
Who decides whether someone is 'insane' for the purposes of the M'Naghten Rules?
The jury, on evidence from two registered medical practitioners (one with relevant expertise). The defence has the legal burden on the balance of probabilities. The special verdict is 'not guilty by reason of insanity'. Disposal options include a hospital order, supervision order, or absolute discharge under the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991 (as amended).
How is 'diminished responsibility' different from 'loss of control'?
Diminished responsibility (Homicide Act 1957 s.2, as amended) requires a recognised medical condition (e.g. depression, autism, PTSD) substantially impairing the defendant's ability to understand conduct / form rational judgment / exercise self-control. Loss of control (Coroners and Justice Act 2009 s.54) doesn't require a medical condition — it requires a qualifying trigger (fear of serious violence OR things said/done giving justifiable sense of being seriously wronged) and that a person of D's sex and age with normal tolerance and self-restraint might have reacted the same way. Both reduce murder to voluntary manslaughter.
What about voluntary intoxication?
Voluntary intoxication is not a defence to crimes of basic intent (assault, criminal damage, most public-order offences) — DPP v Majewski [1977] AC 443. For crimes of specific intent (murder, theft, GBH s.18, burglary), voluntary intoxication can negate the necessary intent, reducing liability to a basic-intent alternative (e.g. murder → manslaughter; s.18 GBH → s.20 GBH). Involuntary intoxication (spiked drink, prescribed medication taken as directed) is treated differently and can negate any mens rea.
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