A person may use reasonable force in self-defence (R v Rose (1884)15 Cox CC 540) and, in extreme circumstances, may be justified in killing an attacker (R v Clegg  1 AC 482 (HL). Reasonable force may be used in defending one's property (Revill v Newbery  1 All ER 291), and if someone intrudes on one's property at night, one might be justified in treating this as a threat not merely to property, but to personal safety. An occupier of premises (even if he is not the owner) and possibly even a licensee (such as a lodger) may use reasonable force against a trespasser What amounts to reasonable force is defined in s 76 Criminal Justice and Immigration Act 2008 as amended by the Crime and Courts Act 2013. In ‘householder’ and other cases the degree of force used by D is not to be regarded as having been reasonable in the circumstances as D believed them to be if it was grossly disproportionate in those circumstances. But, D cannot rely on mistaken belief of the circumstances if the mistaken belief is attributable to self-intoxication. The Criminal Law Act 1967 permits the use of reasonable force in order to prevent crime, to lawfully arrest a criminal or suspected criminal (or to help in arresting him), or to capture someone who has escaped from lawful detention. The Act extends to both police and private citizens. It is not altogether certain whether the statutory right includes the right to kill.
It is a statutory offence to set spring guns or mantraps, except in a private house between sunset and sunrise. One may use a dog in self-defence if this use is reasonable (see guard dog).