The defence of property is a possible justification used by defendants who argue that they should not be held liable for the loss and injury they have caused because they were acting to protect their property. Courts have generally ruled that the use of force may be acceptable, but that lethal force is generally not acceptable in defending property, although it may be acceptable in self-defense or, in some countries, the defense of one's home. As deadly force is not allowed, the setting of booby-traps and the use of dangerous guard dogs is also either not allowed or only allowed on strict terms such as the prominent display of warning notices.
Insofar as an attack on property is a crime, reasonable force may be used to prevent the crime or to arrest the offender, whether it be theft of a sum of money or the damage of an object. In many cases of robbery and burglary, the threat will be to both a person and property, and this combination can be a powerful defence. In AG's Reference (No 2 of 1983) (1984) 1 AER 988 Lane CJ. held that a defendant who manufactured ten petrol bombs to defend his shop during the Toxteth Riots could set up the defence of showing that he possessed an explosive substance "for a lawful purpose" if he could establish that he was acting in self-defence to protect himself or his family or property against an imminent and apprehended attack by means which he believed to be no more than reasonably necessary to meet the attack. In theory, the defence of property by itself cannot reasonably provide a justification for inflicting serious injury, but there are a number of cases approving considerable violence to arrest criminals threatening property.
Although R v Scully (1824) 171 ER 1213 held that it was not justifiable to shoot an intruder merely to arrest him, on the facts, “the life of the prisoner was threatened, and if he considered his life in actual danger, he was justified in shooting the deceased as he had done; but if, not considering his own life in danger, he rashly shot this man, who was only a trespasser, he would be guilty of manslaughter.” See self-defence (Australia) for a comparative view on whether the use of excessive force causing death should give rise to a mitigatory defence and "Reform" below. In Mead and Belt's Case (1823) 68 ER 1006. Holroyd J. instructed a jury that violence could not be used against a civil trespasser, adding: “But, the making an attack upon a dwelling, and especially at night, the law regards as equivalent to an assault on a man's person; for a man's house is his castle and therefore, in the eye of the law, it is equivalent to an assault."
One recent case on using force against a burglar is Anthony Martin v R (2001) EWCA 2245 which resulted in the householder being convicted. As the law currently stands, a person in possession can use no more force than he or she reasonably believes necessary to remove a trespasser from the premises. Further, where the threat to the land or its possession is not immediate and other measures could be taken which would make the use of force unnecessary, e.g. calling the police or seeking remedies through the courts, the defence will normally be lost. But in Chamberlain v Lindon (1998) 1 WLR 1252 Lindon demolished a wall to protect a right-of-way, honestly believing that it was a reasonable means of protecting his property (and, incidentally, avoiding litigation). It was held that it was not necessary to decide whether Lindon’s action was justified as a matter of civil law.
For the purpose of the criminal law, what mattered was whether Lindon believed that his actions were reasonable. Although this case is on the specific interpretation of the statutory defence under s5 Criminal Damage Act 1971, the fact that the defendant was not out of time after nine months of inaction is interesting. On a similar statutory defence, DPP v Bayer and Others (2004) 1 Cr. App. R. 493 dealt with defence of private property as a defence to aggravated trespass under s68 Criminal Justice and Public Order Act 1994.
It was held that if defendants argued that they had used reasonable force to defend property from actual or imminent damage which would constitute a criminal act then the court had to consider whether, on the facts as the defendants honestly believed them to be, the force that had been used was reasonable in all the circumstances. Since the defendants knew that there was nothing unlawful about growing GM maize on the land, defence of property was not available.