8. Necessity and private defence

Necessity is the choice of the lesser of two evils, where the will is not overborne by a threat from a person. Duress of circumstances is the name now given to some of these cases. Bourne, the surgeon who ended the pregnancy of a fourteen-year-old rape victim in order to stop her becoming a physical or mental wreck, is treated as duress of circumstances.

Dudley and Stephens rejected necessity as a defence to murder. Killing the cabin boy so that the others could eat was no defence. The court also disapproved, as a side remark, the idea that drawing lots would make the killing lawful. United States v Holmes had left that direction to a jury after a shipwreck. Self-defence is the obvious exception: killing to save one's own life from an attack is justifiable homicide, not necessity. Dudley is sometimes distinguished where there is no choice of victim. A mountaineer who cuts the rope a second before a falling companion pulls him off the mountain is the example left open. Two swimmers and one plank is left open as well.

Lord Goff has said that a defence of necessity exists at common law, and that its scope is not clear. It can justify what would otherwise be a trespass to land. Edmund Davies LCJ said it is not a defence to murder or to theft. Stealing to relieve hunger does not succeed. Three types are recognised. An act in the public interest, such as destroying property to stop a fire spreading. An act to protect the actor, such as leaving a burning prison. And conduct affecting a person who cannot consent, which is controversial. Re A, the conjoined twins, is the case where the Court of Appeal treated necessity as a defence to what would otherwise be murder. Separation would kill the weaker twin at once. Without it, both would die within weeks. The operation had to be necessary to avoid an inevitable evil, no more than was reasonably necessary, and not disproportionate. F v West Berkshire is the sterilisation of a woman who could not consent, founded on necessity because pregnancy would have been disastrous. Buckoke is Lord Denning's fire engine. Crossing a red light to reach a person at a blazing window is an offence, but he said the driver should be congratulated, not prosecuted.

Private defence is the better name for self-defence. It covers force used for oneself, for another person, and for property. At common law the force must be reasonable and necessary. In England, section 3(1) of the Criminal Law Act 1967 also allows reasonable force in the prevention of crime and in making a lawful arrest. Four questions follow. Was any defensive action necessary? There is no duty, in the English cases, to run away, but the person must show that he does not want to fight. Was the attack reasonably imminent? Force against a future attack is not justified, though anticipatory self-defence is now accepted in some cases. What was the nature and degree of the force? What was the relative strength, and the number, of the people involved?

In Sierra Leone the older retreat rule still applies. The person attacked must retreat as far as he can before he resorts to force. That is not the English law stated in Julien. Julien threw a milk bottle at a man with a chopper. The jury was told he had to retreat first. The conviction was quashed. Lord Widgery said a person threatened need not take to his heels, but must show by his actions that he does not want to fight. Palmer says he may do only what is reasonably necessary. Beckford adds that he need not wait for the first blow. A pre-emptive strike can be justified. The Attorney-General's Reference (No 2 of 1983) allowed a shopkeeper, after a riot, to make petrol bombs against an expected return. Kargbo v R and Bah v R are the local authorities on self-defence. Reasonable force is a question of fact.

Consent may be a defence, but not to every crime. It must be real. It is not real if it is produced by duress or fraud, or if the person lacks capacity. A girl of six cannot consent to sexual intercourse: Howard. Donovan caned a woman who had agreed to a beating. The court rejected consent. Consent is not a defence to injury that is also injurious to the public. Lawful sport is an exception. Ordinary jostling in a poda-poda or a queue is consented to. Aggressive force is not. Euthanasia is an offence. Consent is not a defence to it. Brown holds, by a majority, that willing sado-masochistic injury under sections 47 and 20 is still an offence. Consent works where there is a good reason, such as properly conducted sport. It does not work because the adults agreed.