L9: Criminal Defences
Self-defence, insanity, intoxication, duress and other defences to criminal charges
Criminal Defences
Self-defence, insanity, intoxication, duress and other defences to criminal charges
Key Fact: Defences allow a defendant to avoid criminal liability even if the prosecution has proved actus reus and mens rea
Key Fact: Self-defence is available where the defendant used reasonable force to defend themselves, another person or property
Key Fact: The force used must be proportionate to the threat — excessive force negates the defence of self-defence
Key Fact: Insanity is governed by the M'Naghten rules — the defendant must have a defect of reason from a disease of the mind
Key Fact: Under M'Naghten, the defendant must not know the nature and quality of their act or that it was wrong
Key Fact: Automatism is an act done by the body without the mind's control — it negates actus reus (e.g. sleepwalking, convulsion)
Key Fact: Involuntary intoxication can be a defence if it prevents the defendant forming mens rea — but not for crimes of basic intent
Key Fact: Voluntary intoxication is only a defence to specific intent crimes (e.g. murder, s18 GBH) — not to basic intent crimes
Key Fact: Duress applies where the defendant was compelled to commit a crime by threats of death or serious injury
Key Fact: Duress is not available for murder or attempted murder, and the threat must be immediate and inescapable
Key Fact: Necessity is a rare defence where the defendant breaks the law to avoid a greater evil — it is very strictly limited
Key Fact: Consent can be a defence to some offences — but not to serious harm except in recognised exceptions (sport, surgery)
📋 Key Vocabulary and Concepts
For Criminal Defences, you must know:
- Self-defence: A defence available where the defendant honestly believed they needed to use force and the force used was reasonable in the circumstances
- M'Naghten rules: The legal test for insanity — the defendant must have a defect of reason from a disease of the mind, such that they did not know the nature of their act or that it was wrong
- Automatism: An act performed by the body without the mind's control — if the defendant's mind was not controlling their actions, there is no actus reus
- Duress: A defence where the defendant was forced to commit a crime by threats of death or serious injury to themselves or someone they were responsible for
- Specific intent: Crimes where the prosecution must prove the defendant intended a specific result (e.g. murder, s18 GBH, theft) — voluntary intoxication can be a defence to these
- Basic intent: Crimes where recklessness is sufficient mens rea (e.g. manslaughter, s20 GBH, assault) — voluntary intoxication cannot be a defence to these
❓ Practice Questions
Q: When can self-defence be used as a defence?
Q: What are the M'Naghten rules for insanity?
Q: What is the difference between insanity and automatism?
Q: When can intoxication be a defence?
Q: What are the limitations on the defence of duress?
✅ Answers
- Self-defence is available where the defendant honestly believed they needed to use force and the force used was reasonable and proportionate to the threat perceived. The defendant can defend themselves, another person or property.
- The defendant must have a defect of reason caused by a disease of the mind, such that either (a) they did not know the nature and quality of their act, or (b) they did not know that what they were doing was wrong. Both are objective tests.
- Insanity requires a defect of reason from an internal disease of the mind and leads to a special verdict (not guilty by reason of insanity). Automatism is caused by an external factor and results in a full acquittal, but only if the condition was truly involuntary and not self-induced.
- Involuntary intoxication can negate mens rea for any crime. Voluntary intoxication can only be a defence to specific intent crimes (where the defendant was so drunk they could not form intent) — it is never a defence to basic intent crimes.
- Duress is not available for murder or attempted murder. The threat must be of death or serious injury, it must be immediate or effectively immediate, and a person of reasonable firmness must have succumbed. The defendant must not have voluntarily joined a criminal organisation (the associational rule).
🎯 Exam Tips
- Always identify whether the defence negates actus reus or mens rea — or is a general defence
- Self-defence is a complete defence — know the two-stage test (honest belief + reasonable force)
- The distinction between insanity and automatism turns on internal vs external causes — know this clearly
- Duress limitations are a favourite exam topic — know what crimes it cannot be used for
- Use case names to support your answers where possible — e.g. M'Naghten for insanity, Palmer for self-defence
📝 Exam Technique
GCSE Law Exam Tips — Criminal Defences:
1. For Criminal Defences questions, identify the relevant area of law and state the legal principles clearly
2. Apply legal rules to the facts of the scenario — don't just state the law
3. When evaluating, consider both the effectiveness and fairness of legal rules
4. Reference relevant cases and statutes when discussing Criminal Defences
5. Consider reform proposals and alternative approaches where relevant
1. For Criminal Defences questions, identify the relevant area of law and state the legal principles clearly
2. Apply legal rules to the facts of the scenario — don't just state the law
3. When evaluating, consider both the effectiveness and fairness of legal rules
4. Reference relevant cases and statutes when discussing Criminal Defences
5. Consider reform proposals and alternative approaches where relevant
⚠️ Common Errors
✗ Thinking self-defence allows any level of force ✓ The force must be reasonable and proportionate to the threat — using a weapon against an unarmed attacker may be excessive
✗ Confusing insanity and automatism ✓ Insanity = defect of reason from internal disease of the mind; automatism = external cause making actions involuntary. They have different outcomes (special verdict vs full acquittal)
✗ Saying voluntary intoxication is always a defence ✓ Voluntary intoxication is only a defence to specific intent crimes — it is never a defence to basic intent crimes (e.g. s20 GBH, assault, rape)
✗ Thinking duress is available for all crimes ✓ Duress is not available for murder, attempted murder, or for those who voluntarily associate with criminals (two-gang rule)
✍️ Model Answer
Full-Mark Response
How far do criminal defences achieve justice for defendants? (15 marks)
Criminal defences achieve justice for some defendants by recognising that not all criminal acts deserve punishment, but significant gaps and inconsistencies mean that justice is not always served. Self-defence is an effective defence because it recognises the right to protect oneself and others — the requirement of reasonable force ensures proportionality. However, the test is applied subjectively for the belief and objectively for the force used, which can disadvantage those who genuinely but unreasonably perceive a threat. Insanity, governed by the M'Naghten rules from 1843, is deeply problematic — the archaic language ('defect of reason', 'disease of the mind') is medically meaningless and has led to illogical outcomes where diabetics and epileptics have been classed as insane. The special verdict of 'not guilty by reason of insanity' can result in indefinite hospital detention, which may be more restrictive than a prison sentence — hardly just for a person who was not morally blameworthy. Automatism provides a full acquittal but only where the cause is external, creating an artificial distinction with insanity. Duress recognises that people forced to commit crimes should not always be punished, but the rule excluding murder is controversial — a person threatened with death may have no real choice. Intoxication law is arguably the most unjust area: a defendant who deliberately gets drunk can use this as a defence to specific intent crimes, which many find morally wrong. Furthermore, the burden of proof for most defences falls on the defendant on the balance of probabilities, which may be difficult for vulnerable people. Overall, criminal defences provide necessary recognition that context matters, but their rules are often outdated, inconsistent and fail to achieve justice in too many cases.
📊 AO Deep Dive
Assessment Objective Analysis
AO1 (Knowledge & Understanding): Demonstrate knowledge and understanding of criminal defences, including key legal rules, principles and concepts relevant to OCR J271.
AO2 (Application): Apply knowledge and understanding of criminal defences to legal scenarios and problems, using legal reasoning and analysis.
AO3 (Analysis & Evaluation): Analyse, evaluate and critique legal rules, principles and reform proposals related to criminal defences, constructing balanced and supported arguments.
📝 Exam Questions by Topic
🎬 Video Resources
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