Defences — self-defence, duress, necessity

Criminal law recognises three general defences that negate liability for otherwise criminal conduct: self-defence (justification—the force was lawful), duress (excuse—the defendant's will was overborne by threats), and necessity (residual defence in narrow circumstances). Self-defence requires reasonable force in circumstances as the defendant honestly believed them to be (s 76 CJIA 2008). Duress requires threats of death/serious injury that would overcome a reasonable person sharing the defendant's characteristics, but excludes murder/attempted murder. Necessity remains highly constrained post-Dudley and Stephens, with limited medical exceptions. The rationale balances individual autonomy against societal protection—permitting defensive force and recognising overborne will, whilst maintaining boundaries around the gravest crimes.

Palmer v R [1971] AC 814: Lord Morris established that defendants may use reasonable force to defend themselves in the circumstances they perceive. Foundational pre-codification authority.

Beckford v R [1988] AC 130; R v Williams (Gladstone) [1987] 3 All ER 411: Honest belief in circumstances justifying force suffices, even if unreasonable. Now codified in s 76(4) CJIA 2008.

R v Howe [1987] AC 417: Duress unavailable for murder—the moral gravity of taking life precludes excusing it through threats. Extended to attempted murder in R v Gotts [1992] 2 AC 412.

R v Graham [1982] 1 WLR 294: Established the objective-subjective test for duress: threat of death/serious injury, reasonable belief in threat, reasonable person similarly situated would yield, direct causation, no escape opportunity.

R v Hasan [2005] UKHL 22: Added voluntary association limitation—duress unavailable where defendant associated with criminals knowing risk of compulsion. Significantly narrowed the defence's availability.

Re A (Children) [2001] Fam 147: Recognised limited medical necessity for conjoined twin separation. Brooke LJ's three conditions: act avoids inevitable evil, proportionate response, no alternative.

Courts apply self-defence through s 76's two-stage test: (1) Did defendant honestly believe force was necessary? (subjective—even unreasonable beliefs suffice); (2) Was the force used reasonable in those perceived circumstances? (objective—but judged against defendant's honest belief). For duress, courts assess: immediate threat of death/serious injury; defendant's reasonable belief in threat; whether reasonable person with defendant's characteristics would yield; direct causation; absence of escape routes; no voluntary criminal association. The Hasan limitation proves crucial—prior association with criminals often defeats the defence. Necessity rarely succeeds outside medical contexts—courts demand inevitable evil, proportionate response, and no alternatives. Factual triggers include home intrusions (self-defence), gang coercion (duress), and medical emergencies (necessity).

Students regularly fail by requiring reasonable belief for self-defence—s 76(4) demands only honesty. Many wrongly apply duress to murder, missing the absolute Howe/Gotts exclusion. Confusing duress by threats with duress of circumstances loses marks—the former requires human threats, the latter situational pressure. Overextending necessity beyond Re A's narrow medical exception ignores Dudley and Stephens' enduring constraint. The Hasan voluntary association limit catches many—defendants who join criminal enterprises knowing the risks cannot later claim duress when pressured to offend.