A-Level Law: Criminal Law - Defences

Understanding criminal defences is crucial because they represent the law’s recognition that not all harmful acts should result in punishment. They are the mechanisms through which the justice system acquits individuals who, despite committing the actus reus with the requisite mens rea, acted under circumstances that excuse or justify their conduct. Mastering these defences requires analysing their complex legal boundaries, the delicate balance they strike between individual rights and public safety, and the ongoing debate about their reform in a modern society.

The Justificatory Defence: Self-Defence and the Use of Reasonable Force

Self-defence is a complete defence that justifies what would otherwise be a criminal act. It applies to offences against the person, such as assault or murder. The defence is governed by common law and Section 76 of the Criminal Justice and Immigration Act 2008. For the defence to succeed, you must prove two key elements on the balance of probabilities.

First, you must have genuinely believed that the use of force was necessary to defend yourself or another. This is a subjective test based on your perception of the circumstances, even if that perception was mistaken (R v Williams (Gladstone)). Second, the amount of force used must have been reasonable in the circumstances as you believed them to be. This is an objective test, but the jury must consider that a person acting in the heat of the moment cannot be expected to weigh force to a "nicety" (R v Palmer). The law also now explicitly states that you may use disproportionate, but not grossly disproportionate, force in defence of your home (Section 43 of the Crime and Courts Act 2013, following R v Martin). The critical limitation is that pre-emptive strikes may be justified if an attack is imminent, but revenge attacks are not.

Excusing the Mind: Insanity and Automatism

These defences concern the defendant's mental state at the time of the offence, arguing they were not responsible for their actions.

Insanity is a special defence with roots in the 1843 M’Naghten rules. It is a legal definition, not a medical one. For the defence to succeed, the defendant must prove, on the balance of probabilities, that at the time of the act they were labouring under a "defect of reason" caused by a "disease of the mind". This defect must have made them either: (a) not know the "nature and quality" of their act, or (b) not know that what they were doing was wrong. A "disease of the mind" is any internal condition affecting mental faculties, which can include physical illnesses like epilepsy or diabetes if they cause a malfunction of the mind (R v Sullivan). The major limitation is that a successful verdict results in a special verdict of "not guilty by reason of insanity," which typically leads to a hospital order, making it a risky defence.

Automatism, by contrast, results in a full acquittal. It argues the act was involuntary, performed by muscles without conscious control (e.g., a spasm, reflex, or concussion). The key distinction from insanity is the cause: automatism must be caused by an external factor, such as a blow to the head, the effect of a prescribed drug, or a sneeze. If the cause is internal (a "disease of the mind"), it falls under insanity. For example, in R v Quick, the defendant's automatism due to hypoglycemia (from insulin) was considered external, while in R v Hennessy, hyperglycemia (from the diabetes itself) was an internal "disease of the mind". The defence is not available for self-induced automatism, except in limited cases like non-dangerous prescribed drugs.

Voluntary and Involuntary Intoxication

The law treats intoxication differently depending on whether it was voluntary or involuntary and the type of offence involved. Involuntary intoxication (where the defendant did not know they were consuming an intoxicant) can be a defence to any crime if it negates mens rea. For example, if a spiked drink causes someone to become so drunk they cannot form the intent for theft, the defence may succeed.

Voluntary intoxication (knowingly consuming drink or drugs) is far more limited. For crimes of specific intent (e.g., murder, theft), voluntary intoxication can be a defence if it prevented the defendant from forming that specific intent. The jury asks: "Was the defendant so intoxicated that they could not form the necessary intent?" If yes, they may be acquitted of the specific intent crime but convicted of a lesser basic intent offence (e.g., manslaughter or assault). For crimes of basic intent (e.g., assault, criminal damage), voluntary intoxication is not a defence. The rationale, established in DPP v Majewski, is that getting intoxicated is a reckless course of conduct sufficient for the mens rea of basic intent crimes. A key limitation is that intoxication cannot be used as evidence to support a defence like mistake unless the mistake would have been made even if sober (R v O’Grady).

Duress by Threats, Duress of Circumstances, and Necessity

These defences apply where the defendant claims they were forced to commit a crime.

Duress by threats involves a direct threat from another person of death or serious injury if the crime is not committed. The defence has strict objective and subjective tests from R v Graham (as approved in R v Howe). You must have reasonably believed the threat was imminent and would be carried out (subjective), and a person of reasonable firmality, sharing your characteristics, would have succumbed to the threat (objective). It is not available for murder, attempted murder, or some forms of treason. The threat must be directed at the defendant or their immediate family, and they must have had no safe avenue of escape (R v Hasan).

Duress of circumstances operates on similar principles but arises from objective external circumstances (e.g., driving away from an imminent threat). It was recognised in R v Willer and confirmed in R v Conway. Necessity is a closely related but distinct common law defence, recognised only in very narrow circumstances. It argues the crime was committed to prevent a greater evil. The leading case is R v Dudley and Stephens, which rejected necessity as a defence to murder, though it has been accepted in limited medical and emergency scenarios (e.g., R v Re A (conjoined twins)). The Law Commission has noted the confused overlap between these defences.

Reform Proposals and Critical Perspectives

Many criminal defences are built on centuries-old common law principles, leading to calls for rationalisation and modernisation. The Law Commission for England and Wales has published several reform proposals. Key areas for reform include:

• Insanity and Automation: The Law Commission has criticised the M’Naghten rules as medically outdated and the distinction between internal/external causes as arbitrary and unfair. Proposals suggest replacing "disease of the mind" with a clearer medical basis and creating a new category of "non-insane automatism" for cases of total loss of control.
• Intoxication: The distinction between specific and basic intent is widely seen as illogical and confusing for juries. Reform proposals have included abolishing the Majewski rule and creating a separate offence of "criminal intoxication" or simplifying the rules on when intoxication can negate intent.
• Duress: There is debate about extending duress to cover murder as a defence, rather than just a mitigating factor. The Law Commission has also proposed clarifying and codifying the defences of duress and necessity into a single, coherent statutory defence.

Common Pitfalls

1. Confusing Insanity with Automation: The most common error is misidentifying the cause. Remember: internal cause (e.g., diabetes, epilepsy, sleep disorder) = insanity; external cause (e.g., blow to head, prescribed drug) = automatism. Always identify the source of the mental malfunction first.
2. Misapplying Voluntary Intoxication: Do not argue intoxication negates mens rea for a basic intent crime like assault or criminal damage—it does not. Only use it for specific intent crimes, and remember it can lead to conviction for a lesser basic intent offence.
3. Overlooking the Objective Test in Defences: Many defences, like self-defence and duress, have a crucial objective limb. It is not enough that the defendant believed force was necessary or felt threatened; a reasonable person must also have perceived the situation that way. Failing to apply this objective standard is a critical mistake.
4. Treating Duress and Necessity as the Same: While similar, they have different triggers. Duress by threats requires a human threatener. Duress of circumstances and necessity arise from situational dangers. The case law and availability (especially concerning murder) differ, so precise labelling is essential.

Summary

• Self-defence justifies force that was both subjectively believed necessary and objectively reasonable in the circumstances, with special provisions for defence of the home.
• Insanity (M’Naghten rules) is a legal defence for those with an internal "disease of the mind" causing a defect of reason, leading to a special verdict, while automatism is a full acquittal for involuntary acts caused by an external factor.
• Intoxication: Involuntary intoxication can negate mens rea for any crime. Voluntary intoxication can only negate mens rea for specific intent crimes, not for basic intent crimes.
• Duress (by threats or circumstances) requires a genuine belief in an imminent threat of serious harm and that a person of reasonable firmness would have yielded, but it is not a defence to murder.
• Necessity is a rarely successful defence arguing the crime prevented a greater evil, currently not available for murder.
• The Law Commission has proposed significant reforms to modernise and clarify these defences, particularly regarding insanity, automatism, and intoxication, highlighting their perceived shortcomings in contemporary law.