1 A defence at common law to charges of offences against the person (including homicide) when reasonable force is used to defend oneself, or one's family, or anyone else against attack or threatened attack (R v Rose (1884)15 Cox CC 540). The scope of the defence often overlaps with the statutory right to use reasonable force to prevent a crime (Criminal Law Act 1967 s 3), but also extends to cases in which the statutory right is inapplicable (for example, when the attacker is for some reason not guilty of a crime). There is no rule of law that a person must retreat before acting in self-defence (R v McInnes (1971) 1 WLR 1600). If a person acting in self-defence mistakenly uses more force than was necessary in the circumstances and kills his attacker, he has no defence of self-defence (since the force was not reasonable) and the killing will therefore amount to murder, unless he can show that there was also provocation. However, in deciding whether the force used was justified or reasonably thought to be justified, the jury must bear in mind the difficulty of quickly assessing the correct amount of force to be used. See also general defences.
2 One of the very few bases for a legal use of force under international law. Under Chapter VII (Article 51) of the United Nations Charter, the inherent right of self-defence is preserved. Reference to “inherent right” has promoted the belief that the pre-Charter right of self-defence in customary international law is specifically preserved by the Charter. However, the pre-existing right is arguably wider in scope than that allowed for by the terms of Article 51 and may arguably also allow for anticipatory self-defence. The UK relied on the argument of self-defence in the Falklands Conflict of 1982. See also self-help; use of force.