Criminal Defences in English Law

Introduction

English criminal law recognises a range of defences that may negative liability even where the prosecution has proved the actus reus and mens rea of an offence. Defences may be complete (resulting in acquittal) or partial (reducing murder to manslaughter). The principal defences include self-defence, duress, necessity, automatism, insanity, and intoxication. The burden and standard of proof vary between defences: some must be disproved by the prosecution beyond reasonable doubt, while others must be proved by the defendant on the balance of probabilities.

Self-Defence

Self-defence is a complete defence to any crime involving the use of force, including murder, assault, and criminal damage. The defence also covers the defence of another person and the defence of property. Self-defence is governed by the common law, supplemented by section 76 of the Criminal Justice and Immigration Act 2008, which codifies the principles.

The defence has two elements: the use of force must be necessary in the circumstances as the defendant honestly believed them to be; and the degree of force used must be reasonable in the circumstances as the defendant believed them to be. The test for necessity is subjective: the defendant’s belief need not be reasonable, but the defence is not available if the belief was voluntarily induced by intoxication (R v Hatton (2005)).

The test for reasonable force is partly objective: the question is whether the force used was reasonable in the circumstances as the defendant believed them to be. Section 76(5B) provides that the court must consider that a person acting for a legitimate purpose may not be able to weigh to a nicety the exact measure of necessary action. The householder defence under section 76(5A) provides that force used by a householder in defending their home is not reasonable only if it is grossly disproportionate.

Duress

Duress is a complete defence where the defendant commits a criminal offence because of a threat of death or serious personal injury to themselves or another. The defence is available for all offences except murder, attempted murder, and certain forms of treason. The rationale is that the defendant should not be punished where they acted under such pressure that a person of reasonable firmness would have done the same.

Duress has two elements: the defendant must have reasonably believed in the threat; and a person of reasonable firmness, sharing the defendant’s characteristics, would have responded in the same way. The threat must be of death or serious personal injury and must be directed against the defendant or a person for whom the defendant reasonably feels responsible. In R v Hasan (2005), the House of Lords held that duress is not available where the defendant voluntarily associated with violent criminals and could reasonably have foreseen that they might be subjected to compulsion.

Duress of circumstances is a related defence, available where the defendant commits an offence to avoid a threat of death or serious injury, not arising from human threats but from the circumstances. The same principles apply as to duress by threats.

Necessity

Necessity is a common law defence that justifies conduct that would otherwise be criminal where the defendant acts to prevent a greater evil. The defence is narrower than duress and is not available as a defence to murder, as confirmed in R v Dudley and Stephens (1884), where the court held that necessity could not justify killing and eating a cabin boy to survive shipwreck.

The scope of necessity was considered by the Court of Appeal in Re A (Children) (Conjoined Twins: Separation) (2001), where the court held that the separation of conjoined twins to save the stronger twin was lawful on the basis of necessity, balancing the duty to save life against the duty not to take life. The court also applied the doctrine of double effect, finding that the surgeons’ intention was to save life, not to kill.

Automatism

Automatism is a complete defence where the defendant acts involuntarily, without conscious control of their movements. Automatism may arise from a reflex, a concussion, a sleepwalking episode, or hypoglycaemia (where the diabetic defendant has taken insulin but not eaten). The defendant must prove automatism on the balance of probabilities where the defence is raised.

Automatism is distinguished from insanity based on the cause of the involuntary conduct. If the automatism arises from an internal cause (such as a disease of the mind), the defence is insanity; if it arises from an external cause (such as a blow to the head or an injection), the defence is non-insane automatism, resulting in a complete acquittal. In R v Quick (1973), the Court of Appeal held that hypoglycaemia (low blood sugar caused by insulin and lack of food) was an external cause, while hyperglycaemia (high blood sugar caused by diabetes) was an internal cause.

Insanity

The defence of insanity is governed by the M’Naghten Rules (1843), which provide that a defendant is insane if, at the time of the act, they were labouring under such a defect of reason, from a disease of the mind, as not to know the nature and quality of the act they were doing, or if they did know it, that they did not know they were doing what was wrong.

The M’Naghten Rules have been criticised as outdated and medically inaccurate. The verdict in cases of insanity is not guilty by reason of insanity, which gives the court discretion to make a hospital order, a supervision order, or an absolute discharge.

Intoxication

Intoxication (whether voluntary or involuntary) is not strictly a defence but may negative the mens rea of an offence. Voluntary intoxication is a defence only to offences of specific intent (such as murder, section 18 GBH, theft, and robbery), where the defendant is so intoxicated that they cannot form the required intent. For offences of basic intent (such as manslaughter, section 20 GBH, and assault), voluntary intoxication is not a defence, and the defendant is treated as reckless if they knowingly took an intoxicant (DPP v Majewski (1977)).

Involuntary intoxication — where the defendant did not knowingly take the intoxicant — may be a defence to any offence if it negatives the mens rea, provided the defendant was not reckless as to the nature of the substance consumed.

Conclusion

Criminal defences in English law provide important protections for defendants whose conduct would otherwise be criminal. Self-defence, duress, necessity, automatism, insanity, and intoxication each reflect different policy considerations, balancing the need to punish wrongdoing against the recognition that certain circumstances may justify or excuse otherwise criminal conduct.