Necessity also referred to as duress of circumstance is a defence looking at whether an accused believed on reasonable grounds that the commission of the crime charged was necessary in all the circumstances in order to remove a threat of death or serious injury.
In one case it was held that the defence of duress could not exist for murder however there is case law which has doubted the extent of this decision.
Bayley v Police (2007) was a case which articulated the principles of duress. It was held that the defence can only succeed if it is reasonably possible that an accused believed on reasonable grounds that there was a threat of death or serious injury and that the only they could do was commit the offence. However an alternative course of action must not exist and the response must be proportionate to the danger. If the response is excessive it cannot be said that the accused acted out of necessity.