The defining feature of such a defence is that the situation is not caused by another person (which would fall under either duress or self-defence) and that the accused was in genuine risk of immediate harm or danger.
For the most part crimes that could be justified as necessary are minor in nature, such as driving over the speed limit to reach medical care, or damaging property to escape a fire.
As such the circumstances where necessity could apply to a serious crime are extremely narrow, involving two or more people in an immediately life-threatening situation where only one could survive.
This defence was used in the early trial of Regina v. Dudley & Stephens (1884) 14 QBD 273 DC, where four shipwrecked sailors were cast adrift in a small boat without provisions.
This reflects the distinction between the defences of necessity and duress in that the former is pressure of circumstances arising naturally, whereas the latter is a threat from an entirely human agency that overpowers the will of the defendant.
If hunger was allowed to become the basis of necessity, any poor person might seek to justify burglary to steal food by arguing that he or she had reasonably believed that this was a proportionate response to the threat of malnutrition.
2 of 2004) (2005) EWCA Crim 1415 each defendant appealed convictions associated variously with the cultivation or possession of cannabis resin to be used for pain management.
The difference was restricted to the adverse side effects which, however unpleasant, could not sensibly be said to raise a prima facie possibility of serious injury, let alone one such as would overwhelm the will of the defendant.
Within the limits indicated in Taylor (Joseph) v Lancashire County Council (2005) EWCA Civ 284, the court's decision would involve an evaluation of the medical and scientific evidence, but their conclusion was that this was a policy matter more properly within the remit of the relevant Minister.
The Court of Appeal held that Article 3 ECHR (not to subject a person to inhuman or degrading treatment) does apply to the state.
The state had done nothing to change the defendant's condition for better or worse, and there was nothing to require the court to read the Misuse of Drugs Act 1971 as subject to a defence of medical necessity.
The court applied Quayle where the focus was on Article 8, and the defence of necessity was denied because it would be in conflict with the purpose and effect of the legislative scheme.
Jodie could benefit from the surgery to enjoy probably a near-normal life; refusal to allow separation would result in the death of both twins.