Defences — self-defence, duress, necessity

Defences are the doctrines that justify or excuse otherwise criminal conduct. The principal general defences are self-defence (justification — the defendant''s use of force was lawful), duress (excuse — the defendant''s will was overborne), and necessity (a residual defence available in narrow circumstances). Each has its own substantive test, mens rea framework, and policy considerations.

This week studies the three defences in their modern form. Self-defence: the s 76 CJIA 2008 codification, the Beckford / Williams (Gladstone) honest-belief test, and the proportionality requirement. Duress: the R v Graham / R v Hasan objective-subjective test, the limits on the offences to which duress applies (excluded for murder per R v Howe), and the requirement of immediate threat. Necessity: the Re A (Children) extension to medical situations and the limits on its application beyond emergency contexts.

The topic is part of the Mods Year 1 introduction. The FHS Year 2 module covers the same ground in more detail, including the controversial cases on duress (Hasan; the homicide exclusion) and the relationship between necessity and the homicide cases (the dilemma cases — Dudley and Stephens; Re A).

Self-defence has been recognised at common law since at least the medieval period. The modern test crystallised in Palmer v R [1971] AC 814 (Privy Council), with Lord Morris''s formulation: a person who is attacked may defend themselves and may do what is reasonable to defend themselves; the question is whether the force used was reasonable in the circumstances as the defendant believed them to be. Section 76 of the Criminal Justice and Immigration Act 2008 codified the common-law test with some elaboration.

Duress emerged in the seventeenth and eighteenth centuries as an excuse for offences committed under threat. R v Howe [1987] AC 417 confirmed that duress is not available for murder; R v Gotts [1992] 2 AC 412 extended this to attempted murder. The modern test was articulated in R v Graham [1982] 1 WLR 294 and refined in R v Hasan [2005] UKHL 22.

Necessity has had an unsettled history. The orthodox view (since R v Dudley and Stephens (1884) 14 QBD 273) was that necessity was not a defence, particularly for homicide. Re A (Children) [2001] Fam 147 recognised a limited medical-necessity defence in the context of separating conjoined twins, where one twin would have died without separation. The post-2001 case-law has not significantly extended necessity beyond medical and emergency contexts.

(1) Self-defence — the section 76 framework. Section 76 of the Criminal Justice and Immigration Act 2008 codifies the common-law defence. Section 76(3): the question is whether the degree of force used was reasonable in the circumstances. Section 76(4): the defendant''s belief in the relevant circumstances need not be reasonable, only honestly held (Beckford v R [1988] AC 130; R v Williams (Gladstone) [1987] 3 All ER 411). Section 76(5)–(8) elaborates on the proportionality assessment, including the protection afforded for householders defending against intruders.

Five graded practice questions in the panel below.

See the Further Reading panel for Ashworth, Smith and Hogan, the Law Commission Report on duress, and the post-Hasan academic commentary.