There were 2 conjoined twins, J and M. If they remained conjoined then both would die, while if they were separated only M would die. CA say doctors have a duty to preserve M’s life (i.e. not operate), and duty to save J’s life (i.e. operate). There is a clear difference, regarding necessity, with Dudley and Stephens since in that case D was the judge as to the value of his own life as compared with others. In this case the doctors could make an impartial judgement and therefore decide on the basis of necessity/duress of circumstance that it was worth operating so that at least J would survive.