In English law, the defence of necessity recognises that there may be situations of such overwhelming urgency that a person must be allowed to respond by breaking the law. There have been very few cases in which the defence of necessity has succeeded, and in general terms there are very few situations where such a defence could even be applicable. 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. In almost all cases where a serious crime has taken place, necessity is unlikely to be a successful defence as courts have mostly taken the view that directly harming another person could not be justified even by extreme circumstances unless it directly prevented immediate serious harm or death.[1] Even if a person were already likely to die, and their death would allow others to survive, killing them is not necessary until the point where harm is imminently likely to occur to the others and if that harm is not immediate, then necessity cannot apply. 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. Even in this situation, as the law does allow for a person not to take actions that would save another person if to do so would put their own life at risk, it is seldom strictly necessary for one person to kill another, one allowing the other to die in the course of the situation, then saving themselves.
The Crown Prosecution Service has historically chosen to exercise its discretion not to prosecute those cases where it believes potential defendants have acted reasonably in all the circumstances, and as such where necessity is a strong defence.