Justice demands that a person who is being attacked, or who perceives that he is about to be attacked, should have the right to defend himself. For this reason, both civil and criminal law provide that if a person injures or kills another person while defending himself against an actual or anticipated attack he may, in certain circumstances, escape liability for his act. Unfortunately, though - particularly in civil law - the precise parameters of self-defence have always been somewhat woolly. Although all courts deciding cases in which self-defence has been at issue have agreed on the key requirement that the force used by the defendant must be proportionate to the actual or perceived threat, there has been little examination of the scope of the defence. Recently, however, the House of Lords had the opportunity to review and clarify the nature of self-defence in the high-profile case of Ashley, a tort action which arose from the killing of an unarmed suspect by a police officer who mistakenly believed that the suspect posed an imminent threat. The decision in Ashley - that in civil law, _x000D_ self-defence requires the defendant's belief that he is under serious threat to be both honest and reasonable - is of significance throughout the common law world for the many interesting observations it contains on the differences between civil and criminal law. It is, moreover, of particular interest in Singapore, in light of changes to the Penal Code and proposed changes to the Criminal Procedure Code to limit the criminal liability of police officers who kill or injure suspects during anti-terrorist operations.