The common law defence of necessity operates where circumstances (natural or human threats) bear upon the accused, inducing the accused to break the law to avoid even more dire consequences. There is, thus, some overlapping with the defence of duress. In R v Loughnan  VR 443 at  it was held that the elements of the defence were that —
the criminal act must have been done in order to avoid certain consequences which would have inflicted irreparable evil upon the accused or upon others whom he or she was bound to protect;
the accused must honestly have believed on reasonable grounds that he or she was placed in a situation of imminent peril; and
the acts done to avoid the imminent peril must not be out of proportion to the peril to be avoided.
In R v Cairns  2 Crim App Rep 137, it was held that an accused will have a defence of necessity if —
the commission of the crime was necessary, or reasonably believed to have been necessary, for the purpose of avoiding or preventing death or serious injury to himself or herself, or another;
that necessity was the sine qua non of the commission of the crime; and
the commission of the crime, viewed objectively, was reasonable and proportionate, having regard to the evil to be avoided or prevented.
The accused bears the evidentiary onus of establishing a basis for a defence of necessity and, thereafter, the Crown bears the onus of negativing the defence beyond reasonable doubt: R v Rogers (1996) 86 A Crim R 542, a case in which necessity was taken away from the jury. The suggested direction for Duress [6-150] may conveniently be adapted to the rare case in which the defence of necessity is raised.