Jodie and Mary were ischiopagus conjoined twins (joined at the pelvis) and shared a heart and a pair of lungs. The Court of Appeal was asked to decide whether it was lawful to perform surgery to separate them, when the separation would kill Mary. If the operation did not take place there was evidence that both would die within six months.
The court proceeded on the basis that the potential charge would be murder in that, although the girls were physically joined, they were separate "lives in being". The court decided that the operation would be lawful. Ward LJ. concluded that, by analogy with self-defence, it was lawful to kill Mary because she was, albeit lawfully, killing Jodie. Ward reasoned that causing Mary's death did not breach the public policy of "sanctity of life" because of the "quasi self-defence", but Brooke LJ, rejected self-defence because Mary was not unlawfully threatening Jodie's life. He concluded that necessity rather than duress of circumstances would apply because the doctor's will was not being overwhelmed by the threat. Instead, the doctors were making a rational choice to adopt the lesser of two evils, i.e. the death of one rather than the death of both twins. Ward LJ. reasoned that separation surgery was clearly in Jodie's best interests, but not in Mary's best interests, because it denied her "inherent right to life." Given the conflict of the children's interests and the consequent conflict in the doctor's duties to each child, there was "no other way of dealing with it than by choosing the lesser of the two evils and so finding the least detrimental alternative." 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. So "the least detrimental alternative" was to allow separation.