Necessity
A common law defence rarely recognised in English law. Where the defendant acts to prevent a greater evil, the defence may apply in limited circumstances (Re A (Conjoined Twins) [2001]). Distinct from duress of circumstances, though the boundaries are unclear.
Independent editorial summary — not the official statute text. Read the official version on legislation.gov.uk.
Official College of Policing guidance hosted on GOV.UK describes necessity as closely related to the defence of duress and sometimes legally called duress of circumstances. The guidance illustrates the defence with the classic rock-climbing hypothetical: a climber falls and is left dangling at the end of a rope held by a companion, who must choose between dying alongside them or cutting the rope, accelerating the death of their companion in order to save themselves.
The same guidance sets out the elements an accused must show to raise necessity: that committing the crime was necessary, or the accused reasonably believed it to be necessary, in order to avoid or prevent serious injury or death to himself or another; that they did no more than was necessary for that purpose; and that the commission of the crime, viewed objectively, was reasonable and proportionate having regard to the injury they were seeking to avoid or prevent.
Necessity is treated as a narrow, rarely-invoked defence in English law precisely because of the risk that a broad version of it could be used to justify almost any offence by reference to a supposed greater good — which is why prosecutors are directed to distinguish it carefully from duress by threats (which involves a threat from another person) and to apply it only where the statutory-style conditions above are genuinely met.
Example
A person who breaks into an empty house to escape a life-threatening fire raging outside might raise necessity as a defence to a charge of criminal damage, on the basis that committing the offence was necessary to avoid serious injury or death and was a proportionate response to that danger.
Related terms
Official sources
This explanation is drawn from the official sources below; every substantive statement is verified against them. For advice on a specific matter, see our find help page.