Core principles of criminal liability - General defences

Learning Outcomes

This article outlines the core principles of criminal liability—general defences, including:

• The classification of general defences and the distinction between justification (self-defence) and excuse (automatism, insanity)
• The elements of self-defence at common law and under section 76 Criminal Justice and Immigration Act 2008: necessity, reasonableness, pre‑emptive force, and no duty to retreat
• The different standards in householder versus non-householder cases and the role of honest mistake (excluding intoxication‑induced error)
• The Majewski framework for voluntary intoxication, specific versus basic intent offences, intoxicated mistake, and Dutch courage
• When involuntary intoxication may negate mens rea and why liability remains if mens rea is nevertheless proved (e.g. Kingston)
• The requirements of non‑insane automatism: external cause, total loss of voluntary control, and the effect of self‑induced states
• The contrast between automatism and insanity (internal “disease of the mind”), the M’Naghten test, and consequences (special verdict and disposals)
• Allocation of evidential and legal burdens for each defence and the applicable standards of proof
• Key SQE2 terminology and common exam pitfalls across self-defence, intoxication, and automatism

SQE2 Syllabus

For SQE2, you are required to understand the core general defences to criminal liability and their practical application, with a focus on the following syllabus points:

• the definition and operation of general defences including self-defence, intoxication, automatism, and insanity
• the elements required to successfully rely on each defence
• when justification defences (e.g. self-defence) apply, and when excuse-based defences (e.g. automatism, duress) apply
• the effect of successfully raising a general defence, the burden of proof, and the significance for liability
• section 76 Criminal Justice and Immigration Act 2008: reasonable force “in the circumstances as D believed them to be”, pre-emptive force, no duty to retreat, and householder cases
• voluntary versus involuntary intoxication; specific versus basic intent offences (Majewski); “Dutch courage”; intoxicated mistake; where intoxication still results in liability (e.g. Kingston principle)
• automatism: external cause and total loss of control; contrast with insanity (internal “disease of the mind”) and consequences (special verdict)
• allocation of burdens: evidential burden on D; legal burden on the prosecution to disprove defences beyond reasonable doubt (insanity being the key exception)

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which of the following is a justification defence in criminal law?
   1. automatism
   2. self-defence
   3. insanity
   4. intoxication

2. True or false? Voluntary intoxication provides a defence to any criminal offence.

3. Who bears the evidential burden of proof for raising the defence of self-defence?

4. What is the required test for non-householder self-defence in determining whether force was reasonable?

Introduction

General defences can excuse a defendant from criminal liability or justify the act itself. Key general defences include self-defence, intoxication, automatism, and insanity. For SQE2, you need to know the requirements for each, their practical scope, and how they affect criminal responsibility. Understanding these defences is essential for effectively evaluating criminal scenarios and advising clients.

Self-defence (including defence of another and defence of property) operates at common law and is reflected in statute when preventing crime or assisting lawful arrest. Intoxication is not a true defence but may operate to negate mens rea in restricted circumstances. Automatism concerns the voluntariness of conduct. Insanity focuses on cognitive capacity arising from a disease of the mind and produces a special verdict with specific disposals.

General Justification and Excuse Defences

General defences apply to a wide range of criminal offences and can operate as either justification or excuse. Justification defences (such as self-defence) render the act lawful. Excuse defences (such as automatism or insanity) acknowledge wrongdoing but excuse the defendant because of their condition or circumstances.

Key Term: justification defence
A defence that, if established, renders the defendant's action lawful and removes criminal liability.

Key Term: excuse defence
A defence that, if established, recognises that the defendant's act was wrong but excuses them from liability due to their situation or capacity.

The practical distinction matters when explaining outcomes. A successful justification typically results in a complete acquittal and communicates that the conduct was permissible in the circumstances. An excuse acquits because the actor is not blameworthy, even though the conduct remains wrong in principle; insanity is an example with a distinct procedural outcome (special verdict).

The Defence of Self-Defence

Self-defence, also called private defence, allows a person to use reasonable force to protect themselves, others, or property, or to prevent a crime.

Key Term: self-defence
A general defence available where a person uses reasonable force in the circumstances as they honestly believed them to be, for the protection of self, others, or property, or to prevent crime.

To rely on self-defence:

1. The force must be necessary on the facts as the defendant honestly believed them to be.
2. The force must be reasonable and not excessive in the circumstances.

The statutory framework for assessing reasonableness in England and Wales is set out in section 76 Criminal Justice and Immigration Act 2008. That section does not create the defence but clarifies key principles:

• The necessity of force is assessed subjectively: did D honestly believe force was necessary? An honestly held belief can be mistaken; if so, D is judged on the facts as they believed them to be.
• The degree of force is assessed objectively but in light of D’s honest belief of the circumstances.
• There is no duty to retreat; failing to retreat may be relevant but is not determinative.
• D may act pre-emptively where an attack is imminent; the law does not require waiting to be struck first.
• Force is not to be weighed to a nicety in the heat of the moment; the question is whether D did what was reasonable in the circumstances.
• If a mistake is due to voluntary intoxication, D cannot rely on that mistake to justify force.

In prevention of crime or to assist in lawful arrest, reasonable force may be used under section 3(1) Criminal Law Act 1967, with the same section 76 standards on reasonableness applying.

Householder cases: Where the force is used by a householder against a trespasser in a dwelling at night or otherwise, the law recognises the heightened stress and fear faced. In such cases, the force may be disproportionate yet still reasonable; however, grossly disproportionate force is never reasonable. For non-householder cases, force must simply be reasonable, and disproportionate force is ordinarily unreasonable.

Worked Example 1.1

Sophie is attacked late at night. She reasonably believes her attacker is armed. She strikes him with a bottle, causing injury.

Answer:
If Sophie honestly believed force was necessary, and the force was not excessive for her genuine belief, she may rely on self-defence—even if her belief was mistaken, provided it was honestly held.

Assessing necessity: If D is the aggressor, they may still rely on self-defence if the original victim’s response becomes so out of proportion that the roles effectively reverse and D then acts to protect themselves. Pre-emptive strikes can be justified where an attack is imminent. Carrying a weapon in anticipation of imminent violence can be consistent with self-defence, but the ultimate question remains whether, at the moment force was used, it was necessary and reasonable.

Assessing reasonableness: Relevant factors include the seriousness of the threat, whether D or others faced a weapon, the speed of events, the relative size/strength of the parties, and the possibility of escape. In householder scenarios, the law allows a margin of error greater than in non-householder cases, but not to the point of gross disproportionality.

Worked Example 1.2

At 2 a.m., Maya is awoken by noises downstairs. She confronts a masked intruder in her kitchen, grabs a heavy ornament and strikes him once as he advances towards her. The blow fractures his skull.

Answer:
This is a householder situation. The force may be disproportionate yet still reasonable given the perceived threat in her home at night. The single pre-emptive strike as the intruder advanced is unlikely to be grossly disproportionate. The defence should be left to the tribunal of fact applying the section 76 standards.

Exam Warning

In self-defence, the reasonableness of force is assessed objectively but in the circumstances as the defendant honestly believed them to be, not as they actually were. An honest but unreasonable mistake may still allow the defence. However, a mistake induced by voluntary intoxication cannot be relied upon to justify the use of force.

Intoxication as a Defence

Intoxication can impact liability only in certain cases.

Key Term: intoxication
A state resulting from voluntary or involuntary consumption of alcohol or drugs, sometimes affecting the defendant's mental state required for an offence.

• Voluntary intoxication is typically not a defence for crimes of basic intent where recklessness suffices for the mens rea. It may provide a defence to crimes of specific intent if, due to intoxication, the defendant did not form the required intent.
• Involuntary intoxication (where intoxication was not the defendant's fault) can provide a defence to both specific and basic intent crimes if the defendant did not form the required mens rea.

Key Term: specific intent offence
An offence where intention is the only form of mens rea that satisfies liability (e.g., murder, theft).

Key Term: basic intent offence
An offence where recklessness or intention is sufficient for liability (e.g., assault, criminal damage).

In applying the distinction:

• Voluntary intoxication may negate intention for a specific intent offence (e.g. s 18 OAPA 1861, murder, theft, robbery, burglary under s 9(1)(a) where intention to commit one of the listed offences at entry is required). Where intent is not proved because of intoxication, a conviction for a lesser basic intent alternative may still follow if charged in the alternative (e.g. s 20 instead of s 18).
• For basic intent offences (e.g. s 47, s 20 OAPA, criminal damage, common assault, sexual assault), voluntary intoxication is no defence. Becoming intoxicated is treated as reckless conduct supplying the mens rea.
• Involuntary intoxication (e.g. a spiked drink or an unexpected reaction to a properly taken non-dangerous prescription drug) can negate mens rea for any offence. However, if the prosecution proves that D actually formed the mens rea despite the involuntary intoxication, there is no acquittal.

Intoxication interacts with other defences. For self-defence, a mistaken belief in the need for force caused by voluntary intoxication cannot be relied upon. For automatism, intoxication with dangerous drugs or alcohol does not found automatism; self-induced states may bar the defence for basic intent offences.

Key Term: dutch courage
Becoming intoxicated deliberately to summon courage to commit an offence. This never affords a defence; the intent is treated as having been formed before intoxication.

Worked Example 1.3

Ahmed gets very drunk and then punches a stranger, breaking his nose. He claims he was so intoxicated he did not intend harm.

Answer:
Voluntary intoxication is not a defence to basic intent offences like assault occasioning actual bodily harm, because recklessness (which is presumed by choosing to get intoxicated) suffices.

Worked Example 1.4

Priya’s drink is unknowingly spiked with a strong sedative. Disinhibited and confused, she picks up a handbag believing it to be hers and leaves a bar.

Answer:
This is involuntary intoxication. If Priya did not form the necessary mens rea (dishonesty and intention to permanently deprive), she should be acquitted of theft. If the prosecution can prove she nevertheless formed that mens rea at the time, intoxication does not excuse.

Worked Example 1.5

Leo decides to “build up courage” by drinking a bottle of whisky before stabbing a rival. He later claims he was too drunk to form intent to cause grievous bodily harm.

Answer:
This is a “Dutch courage” situation. The law treats Leo as having intended the offence notwithstanding his intoxication. Intoxication cannot negate intent deliberately sought through drinking to commit the crime.

Exam Warning: Intoxication

Involuntary intoxication is only a defence where the defendant actually lacked mens rea at the relevant time. If mens rea is proved, intoxication (even if involuntary) does not excuse the defendant. Voluntary intoxication cannot found a mistaken belief for self-defence.

Additional points to be aware of:

• Self-induced intoxication through non-dangerous substances (e.g. an unusual reaction to a prescribed drug taken correctly) may negate mens rea. If, however, D knew of a risk of aggression or impairment and took the substance regardless, the court may treat that as reckless.
• Sexual offences are treated as basic intent for intoxication purposes. Voluntary intoxication is no defence where intention is not required beyond recklessness or voluntariness of the sexual act.

The Defence of Automatism

Automatism refers to situations where the defendant had no conscious control over their actions due to an external factor.

Key Term: automatism
A complete defence where a defendant's actions were wholly involuntary due to an external cause, so there is no actus reus.

Core requirements for non-insane automatism:

• A total loss of voluntary control over bodily movements. Partial impairment, or an inability to resist impulses, is insufficient.
• The loss of control must be caused by an external factor (e.g. concussion from a blow to the head, the unexpected effect of a properly taken non-dangerous drug, a swarm of bees entering the car).
• D must not have been at fault in bringing about the automatism. Where D foresaw or ought to have foreseen the risk of entering an automatic state (e.g. by failing to eat after insulin or starting to drive when very tired), a defence is unlikely for basic intent crimes.

Automatism differs from insanity, which involves an internal cause. If a defendant is acting in a genuinely automatic state caused by, for example, a blow to the head or a reaction to a drug, and was not at fault in putting themselves in that position, they are likely to be acquitted.

Worked Example 1.6

Carla suffers a seizure due to undiagnosed epilepsy and attacks someone, having no control or awareness at the time.

Answer:
If the seizure was due to an internal factor (like epilepsy), the correct defence is insanity, not automatism. If an external factor caused her loss of control, automatism may apply.

Key Term: insanity
A complete defence available where, due to a disease of the mind, the defendant was unable to understand the nature or quality of their act or that it was wrong.

Key Term: disease of the mind
A legal concept, not a medical diagnosis, referring to a malfunctioning of the defendant's mind caused by an internal condition.

Common contrasts:

• Hypoglycaemia (low blood sugar caused by insulin) typically arises from an external agent and may support automatism if there was a total loss of control and no fault in inducing the state.
• Hyperglycaemia (high blood sugar due to an internal condition) is treated as an internal malfunction and aligns with insanity.

Self-induced automatism: If D knows that failing to eat after insulin may cause loss of control but drives anyway and then loses control, a defence to a basic intent offence is unlikely because D’s conduct is reckless. The position for specific intent offences is more fact-specific: the question remains whether the mens rea was in fact formed.

Worked Example 1.7

Nadia, a diabetic, injects insulin and forgets to eat before driving. She blackouts and crashes, injuring another driver.

Answer:
If the blackout was foreseeable and caused by her own fault in failing to eat, automatism is unlikely to succeed for basic intent offences because driving in that state would be reckless. If the episode was entirely unexpected and there was a total loss of control, the tribunal of fact will evaluate automatism against the evidence.

Revision Tip

Always distinguish between automatism (external cause) and insanity (internal cause) when answering exam scenarios.

Insanity: Although this article focuses on the automatism/insanity divide within the automatism section, the (M’Naghten) insanity test requires D to prove on the balance of probabilities that, at the time of the act, they were suffering from a defect of reason, arising from a disease of the mind, such that they did not know the nature and quality of the act or did not know it was wrong. The outcome is a special verdict of “not guilty by reason of insanity”, after which the court selects an appropriate disposal (e.g. hospital order, supervision order, or absolute discharge), depending on the offence and current statutory framework.

The Burden of Proof for General Defences

Generally, the defendant bears the evidential burden to raise a possible general defence. Once the defence is raised on the evidence, the prosecution must disprove it beyond reasonable doubt.

Key Term: evidential burden
The obligation on a party to adduce sufficient evidence to make a defence a real issue in the case.

Key Term: legal burden
The obligation on a party to prove an issue in the case to the required standard—usually the prosecution to prove guilt beyond reasonable doubt, unless a specific defence (e.g., insanity) places the legal burden on the defendant.

For self-defence and automatism, the defendant need only raise some evidence capable of supporting the defence; if they do, the tribunal of fact must be directed to consider it unless the evidence is truly fanciful. The prosecution must then make the tribunal of fact sure that the defence does not apply.

In intoxication, the prosecution still bears the legal burden to prove the requisite mens rea. Where D relies on intoxication as negating mens rea, the tribunal of fact examines whether mens rea was in fact present. The legal burden is not reversed.

Exam Warning: Burden of Proof

For insanity, the legal burden is on the defendant to prove the defence on the balance of probabilities. For self-defence, the defendant has only the evidential burden; the prosecution must then disprove the defence beyond reasonable doubt.

Summary Table: General Defences Compared

Note: Intoxication is not a standalone defence; it operates by potentially negating mens rea. Insanity produces a special verdict rather than a conventional acquittal, with disposals governed by statute. Self-defence encompasses defence of others and property and the prevention of crime; the reasonableness inquiry is undertaken in the light of D’s honest belief of the circumstances.

Key Point Checklist

This article has covered the following key knowledge points:

• General defences include self-defence, intoxication, automatism, and insanity.
• Self-defence is a justification requiring necessity and reasonableness of force. There is no duty to retreat; pre-emptive force may be justified. Householder cases allow disproportionate (but not grossly disproportionate) force; non-householder cases require simply reasonable force.
• The reasonableness of force is judged objectively in the circumstances as D honestly believed them to be. A mistake caused by voluntary intoxication cannot be relied upon.
• Voluntary intoxication rarely provides a defence; it may negate intent for specific intent offences but is no defence to basic intent offences. Intoxication used for “Dutch courage” never exculpates.
• Involuntary intoxication can exculpate if mens rea was not formed. If mens rea is proved despite intoxication, there is no defence (even if intoxication was involuntary).
• Automatism requires a total loss of voluntary control due to an external cause and no fault in inducing the state; self-induced automatism will commonly fail for basic intent offences.
• Insanity arises from an internal disease of the mind and requires proof by D on the balance of probabilities; the outcome is a special verdict with tailored disposals.
• The burden of proof varies: for self-defence, automatism, and intoxication, the prosecution must disprove the defence beyond reasonable doubt when properly raised; for insanity, the defendant bears the legal burden on the balance of probabilities.
• Understanding the requirements and limits of general defences is critical for problem scenarios, including identifying the right label (automatism versus insanity) and applying section 76 CJIA 2008.

Key Terms and Concepts

• justification defence
• excuse defence
• self-defence
• intoxication
• specific intent offence
• basic intent offence
• automatism
• insanity
• disease of the mind
• evidential burden
• legal burden
• dutch courage