Necessity, private defence and the killing of Mary

This article examines the reasons used by the Court of Appeal in Re A (Children) to authorise and justify an operation which would inevitably kill the weaker of a pair of conjoined twins in order to offer the stronger twin a good chance of a long and happy life. The crux of the judgment was that a utilitarian theory of necessity could justify this operation. This article seeks to define the criminal law defences at issue in the case and to argue that utilitarian necessity is such a dangerous doctrine that it should never be employed if there is any other defence which can be made to serve the same purpose--as there was in the present case.