# General defences in criminal law: overview

> **Key takeaway:** Self-defence: honest belief + reasonable force (CJIA 2008 s.76). Duress: tight test; not for murder (Howe). Intoxication: Majewski basic vs specific intent. Insanity: M'Naghten; automatism differs. Partial homicide defences are separate.

- **Jurisdiction:** England & Wales
- **Practice area:** Criminal
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/Criminal/general-defences
- **Keywords:** general defences, self-defence, duress, intoxication, Majewski, insanity, M'Naghten, CJIA 2008 s.76, Howe

## What is this about?

General defences may defeat liability even where actus reus and mens rea appear present. This overview maps the principal common-law and statutory defences used across offences — self-defence, necessity/duress, intoxication, insanity/automatism, and mistake — without replacing offence-specific partial defences (e.g. loss of control, diminished responsibility).

## What is the core rule?

Self-defence and defence of others/property (Criminal Justice and Immigration Act 2008 s.76; common law) require an honest belief in circumstances making defence necessary and force reasonable in those circumstances (householder cases have a modified reasonableness threshold). Duress of threats may excuse where a reasonable person would have yielded, subject to tight limits (no duress to murder — Howe). Intoxication: voluntary intoxication may negate specific intent but not basic intent (Majewski); involuntary intoxication is treated more favourably. Insanity (M'Naghten) and non-insane automatism are distinct; sane automatism may yield acquittal, insanity a special verdict.

## What are the elements or test?

1. Identify the defence pleaded and whether it is offence-general or partial/specific
2. Self-defence: honest belief in facts; necessity of force; reasonableness of degree (s.76 CJIA 2008)
3. Duress: threat of death/serious injury; causative; reasonable steadfastness; no safe avenue; not self-induced; unavailable for murder
4. Intoxication: voluntary or involuntary; specific vs basic intent offence?
5. Insanity vs automatism: internal disease of mind (M'Naghten) vs external factor; evidential burdens

## Which authorities matter?

- **Criminal Justice and Immigration Act 2008, s.76** — Statutory confirmation and guidance on reasonable force in self-defence, including householder cases.
- **R v Howe [1987] AC 417** — Duress is not a defence to murder.
- **DPP v Majewski [1977] AC 443** — Voluntary intoxication is no defence to basic-intent crimes.
- **M'Naghten's Case (1843) 10 Cl & F 200** — Classic rules for the insanity defence: defect of reason from disease of the mind, such that the defendant did not know the nature and quality of the act or that it was wrong.

## How does this apply in practice?

This is a map, not a full treatise on each defence. Sexual offences, homicide partial defences, and self-defence in domestic abuse contexts need specialised authorities (including householder and DA context guidance). Always check the indictment offence before applying Majewski classifications.

## What are common pitfalls?

- Running duress to murder despite Howe
- Treating voluntary intoxication as a general excuse
- Confusing legal insanity with medical diagnosis alone
- Applying self-defence reasonableness to the facts as the jury finds them without the s.76 honest-belief framework

## When would a practitioner use this?

First-pass defence analysis for charging advice, plea strategy, and summing-up preparation.

## Quick reference

Self-defence: honest belief + reasonable force (CJIA 2008 s.76). Duress: tight test; not for murder (Howe). Intoxication: Majewski basic vs specific intent. Insanity: M'Naghten; automatism differs. Partial homicide defences are separate.

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*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*