On Private Defence, from the Textbook of Criminal Law

This post contains extracts from Chapter 23 Private Defence of Textbook of Criminal Law by Glanville L Williams (2nd Ed 1983).


In general, private defence is an excuse for any crime against the person or property. It probably applies to the defence even of a stranger, and may be used not only against culpable but against innocent aggressors.

In general, defence is allowed only when it is immediately necessary against threatened violence. A person who acts under a mistaken belief in the need for defence is protected, except that the courts hold that the mistake must be reasonable. The best that can be said of this qualification is that it is construed leniently, at least in favour of the forces of order. On principle, it should be enough that the force used was in fact necessary for defence, even though the actor did not know this; but the law is not clear. There is no duty to retreat, as such, but even a defender must wherever possible make plain his desire to withdraw from the combat. The right of private defence is not lost by reason of the defender's having refused to comply with unlawful commands.

The force used in defence must be not only necessary for the purpose of avoiding the attack but also reasonable, i.e. proportionate to the harm threatened; the rule is best stated in the negative form that the force must not be such that a reasonable man would have regarded it as being out of all proportion to the danger. The question of proportionality is for the jury. A person may lawfully threaten more force than he would be allowed to use.

The carrying of firearms and other offensive weapons is generally forbidden, but (1) a thing is not an "offensive weapon" if it is not offensive per se and is carried only to frighten; (2) a person does not "have it with him" if he merely snatches it up in the emergency of defence, and (3) there is the defence of "reasonable excuse" where the defendant acted reasonably under an "imminent particular threat affecting the particular circumstances in which the weapon was carried."

An arrester need not give back, and the right of self-defence may entitle him in the last resort to kill a resisting criminal when he could not lawfully kill a fleeing criminal.

The right of defence avails against the police if they act illegally, but the defender cannot take benefit from a mistake as to the law of arrest or self-defence. It was held in Fennell that a person who rescues another from police detention does so at his peril of the detention being lawful, and cannot set up a mistake of fact.

The occupier of premises may use necessary and reasonable force to defend them against a trespasser, or one reasonably thought to be a trespasser; and it seems that even a licensee (such as a lodger) can eject trespassing strangers. It is a statutory offence to set spring guns or man-traps, except in a dwelling-house between sunset and sunrise. It has not been decided whether the exception operates to confer an exemption from the ordinary law of offences against the person. Such defences as spikes and dogs are lawful if reasonable. Guard dogs must, by statute, be kept under full control, except in private houses or on agricultural land.

The traditional rule is that even death may be inflicted in defence of the possession of a dwelling; and in Hussey this was applied even where the aggressor was acting, and was known to be acting, under a claim of right.

A displaced occupier who uses violence to re-enter upon premises commits an offence under the Criminal Law Act 1977, apart from the displaced residential (or intending residential) occupier, who is given exemption. The latter may, therefore, use necessary and reasonable force to re-enter.

Necessary and reasonable force may also be used to prevent unlawful damage to chattels, or to prevent their dispossession. According to Blades v. Higgs, it may be used even against a person who is known to claim the right to retain the goods, if the claim is invalid.

Another form of lawful self-help is in respect of abatement of nuisance.

23.2 The Necessity for Defence

The defence of private defence resembles that of preventing crime in the twin requirements that the act must be immediately necessary (there must be no milder way of achieving the end) and proportional to the harm feared. Both questions, the factual and the evaluative, are frequently left to the jury as a single, unanalysed, question of reasonableness. This saves the trouble of sorting them out, but may lead to regrettable confusion.

A behaves aggressively towards B; B squares up to him and A makes to retreat, showing clearly that he has thought better of attacking. A blow given him by B cannot be justified, because the necessity for defence has passed.
A is about to slap B's face; B is a weakling who can avoid the slap only by using a gun. B is not justified in shooting, but must submit to being slapped.
On the necessity question, is a pre-emptive strike allowed?

It is sometimes thought that defence is allowed only against immediately threatened violence. Clearly, force may not be used to meet a threat of violence in the future, when there is still time for the person threatened to seek police protection. If he acts prematurely the judge may perhaps withdraw the defence from the jury, on the ground that there was no evidence of necessity when the defendant acted. But, as was said before in connection with the prevention of crime, there: is a distinction between the immediacy of the necessity for acting and the immediacy of the threatened violence. The use of force may be immediately necessary to prevent an attack in the future. If, for example, there is a present hostile demonstration indicating that violence is about to be used, the defender finger on the trigger. Moreover, force may lawfully be threatened in advance of the immediate necessity for using it. For these reasons it is best to regard the question of the immediacy of the threat as something that enters into the calculation of necessity, rather than as an independent rule

The requirement of reasonableness is unhappy. Enough has been said in criticism of it, and the CLRC has recommended that it should be expunged from the law. In practice, as we have seen, the requirement may be construed indulgently to the defendant, for, as Holmes J memorably said in the United States Supreme Court, "detached reflection cannot be demanded in the presence of an uplifted knife." As we shall see in the next section, the requirement is now stated in such mitigated terms as to cast doubt on whether it still forms part of the law.

Can one act in self-defence by accident, so to speak? That is to say, without knowing that the other is himself about to attack you?

The question is unlikely to present itself in that form, but it may arise somewhat differently. Suppose that D acts, as he believes, in self-defence. He is prosecuted for the injury he inflicts, and it is argued for the prosecution that although he may have believed in the necessity for self-defence he had no reasonable grounds for the belief. However, the evidence shows that in fact he was under such a necessity, for reasons that he did not know at the time. This is the same problem as was mentioned in relation to arrest, and the same answer should be given. If there is in fact a case for acting in self-defence, the investigation into the legality of the act should be foreclosed. The defendant's action is lawful irrespective of what the defendant believed or of the grounds of his belief. The law would be oppressive if it said: It is true that you took this action because you felt it in your bones that you were in peril, and it is true that you were right, but you cannot now assign reasonable grounds for your belief, so you were only right by a fluke and will be convicted.

If a person is set upon, is he obliged to try to run away, if he can, instead of acting in self-defence?

The law now is that he is not under a duty to retreat as such, but he must take any opportunity of disengaging himself. The Court of Appeal formulated the rule in the following terms.

"It is not, as we understand it, the law that a person threatened must take to his heels and run in the dramatic way suggested by counsel for the appellant; but what is necessary is that he should demonstrate by his actions that he does not want to fight. He must demonstrate that he is prepared to temporise and disengage and perhaps to make some physical withdrawal; and that that is necessary as a feature of the justification of self-defence is true, in our opinion, whether the charge is a homicide charge or something less serious."


In the example of the proportionality rule given at the beginning of 23.2 the use of the gun may be "necessary" to avoid the apprehended evil of being slapped, but it is disproportionate to that evil, and therefore unlawful. "For every assault it is not reasonable a man should be banged with a cudgel" (Holt CJ). The proportionality rule is based on the view that there are some insults and hurts that one must suffer rather than use extreme force, if the choice is between suffering the hurt and using the extreme force. The rule involves a community standard of reasonableness and is left to the consideration of the jury. It can bear hardly on the defender, but much depends on the way in which judges and juries administer it; and that, again, may depend on whether they happen to empathise with the frightened defender or with his injured (or dead) assailant. If the defendant's reaction was disproportionate, the attack he feared or was resisting will go only in mitigation.

The previous examples of the proportionality rule are too trivial to be helpful. The real-life problem arises where a person is fiercely attacked by a bully whom he can resist only by the use of a lethal weapon. It is now so common for brutal men to kick their opponent about the head after he has been felled to the ground that anyone who is attacked may reasonably dread this possibility.

In order to give proper width to the right of self-defence an Australian court stated the law negatively: "Would a reasonable person in the defendant's situation have regarded what he did as out of all proportion to the danger to be guarded against?" A somewhat different approach to the problem was adopted by the Court of Appeal in Shannon, basing itself on the following dictum of Lord Morris:

"A person defending himself cannot weigh to a nicety the exact measure of his necessary defensive action. If a jury thought that in a moment of unexpected anguish a person attacked had only done what he honestly and instinctively thought was necessary that would be most potent evidence that only reasonable defensive action had been taken."

Approving this statement, the Court of Appeal quashed a conviction because the trial judge had not conveyed the point to the jury and had not directed them broadly in Lord Morris's words. The real issue, the court thought, was: "Was this stabbing within the conception of necessary self-defence judged by the standards of common sense, bearing in mind the position of the defendant at the moment of stabbing, or was it a case of angry retaliation or pure aggression on his part?" In future, an instruction to the jury in these terms will evidently be necessary in many cases of self-defence.

The facts of Shannon were that the deceased, a heavily built man who had convictions for violence, had been making threats against Shannon for having (as he believed) "grassed" him. Shannon, who had no history of violence or aggression, must have been living in fear of an attack for some time. When the attack came he fought back, the fight (though evidently largely one-sided) being described by a bystander as "pretty frightening." Shannon's evidence was that he was being held very tightly by the neck and was being dragged down and "kneed;" he feared that if he fell while in the grip of his attacker he would have "got beat up by his feet." He lashed out with a scissors and inflicted a fatal blow. On the issue of self-defence the judge left the case to the jury with the bald question: Did the defendant use more force than was necessary in the circumstances?" On this the jury, surprisingly, returned a conviction of manslaughter. The conviction was quashed, as already said, for inadequate direction to the jury; but the Court of Appeal expressed no other criticism of the verdict. We are left with the impression that if in a similar case the judge reads out Lord Morris's dictum to the jury, who nevertheless convict, the conviction will stand.

On the dictum, it is not easy to see how "what the defendant thought" could be evidence of what it was reasonable for him to do. The usual opinion is that the question what is reasonable, in the multifarious applications of that word, is for the unaided vote of the jury, and is not a matter for "evidence" in the ordinary way. It looks very much as though the dictum is a way of escaping from the test of reasonableness without acknowledging the fact. This conclusion is strengthened by the above-quoted remark of the Court of Appeal, which (epitomising a lengthy statement of Lord Morris) distinguishes sharply between "necessary self-defence" on the one hand and "angry retaliation or pure aggression" on the other. The dichotomy allows no place in between for unnecessary but putative self-defence. All putative self-defence, it seems, falls into the category of "necessary self-defence." In this part of the judgment, the idea that the defendant's belief is merely evidence of reasonableness has suddenly vanished; indeed, the very word "reasonable" is dropped. It seems, therefore, that the decision makes a radical change in the law. At least where the defender fears death or serious injury, there is no proportionality rule any longer; and a good thing too---in view of the jury's verdict in Shannon. German law, it seems, gets on without a proportionality rule, and so could we, where the facts are similar to those in Shannon. The reasoning in the decision is fudged, but that is the price one pays for a beneficial change in the law.

Suppose Shannon had used his scissors upon a mugger; would the view of the court have been the same?

If the thief were trying to drag his bag from him, and the victim of the robbery stabbed the thief merely in order to avoid losing his property, the authorities give no indication of the legal position. All that one can clearly do by way of defence against robbery is to give the robber blows and threaten him with a weapon.6 For some reason that is not clear, the courts occasionally seem to regard the scandal of the killing of a robber (or of a person who is feared to be a robber) as of greater moment than the safety of the robber's victim in respect of his person and property. Possibly, if the matter were fully argued, the court would apply the same rule as in Shannon, but one does not know. The jury's verdict in Shannon is a standing warning to all defenders of the legal danger of killing an adversary, even in self-defence.

To what extent can one carry weapons by way of defence? Could I carry a hefty spanner to use if I am attacked on the street at night?

Not legally. It is, you will remember, an either way offence under the Prevention of Crimes Act 1953 section 1 for a person to have "with him" an offensive weapon in a public place without reasonable excuse.

Offensive weapons are (1) those that are offensive per se,9 and (2) those that are capable of an innocent use (your spanner) but are carried for the purpose of causing injury to the person. It does not matter that the injury contemplated will be defensive.

But you said that reasonable excuse is a defence. Why isn't self-defence a reasonable excuse?

We are not allowed to make a habit of carrying a weapon for defence because every weapon could be used for that purpose, and the excuse could be used by thugs as well as by honest men. The defence of reasonable excuse is available, but is given a restricted interpretation; it might justify a man in carrying a weapon after being attacked within the last day or two, or perhaps for a little longer; but even the fact that he has been mugged does not give him an indefinite licence to carry a weapon. There must be "an imminent particular threat affecting the particular circumstances in which the weapon was carried." The question of reasonable excuse is one for the jury or magistrates, but the magistrates, at least, will be expected to guide themselves by the above principle stated by the higher courts.

By the way, if you carried the spanner without any intention to strike anyone with it, but only to frighten off an attack, it would not be an "offensive weapon," not being offensive per se and not being carried for the purpose of causing injury." And if you did not intend to strike anyone with the spanner when you carried it, but used it on the spur of the moment when attacked, it would still not be an "offensive weapon" and you would still not be guilty of having it with you for an offensive purpose.

Again, you would not commit an offence under the Act of 1953 if you used a spanner that you snatched from an assailant in order to strike him, or one that you happened to see when you were being attacked, for the same reason as before---would not be an "offensive weapon" and you would not "have it with you." These two escape-routes from the Act (depending on an understanding of what is an offensive weapon and when the user had it "with him") are quite distinct from the question of what is a reasonable excuse. Are guns in the same position?

Most guns are offensive weapons within the Prevention of Crimes Act, and, in addition, the private possession of firearms is strictly controlled under the Firearms Act 1968 and other Acts. Even if you have a licence from the police to possess a firearm, carrying the weapon is an offence under section 19 of the Act, except that the courts will allow the statutory defence of "reasonable excuse," which is construed in the same way as in the Prevention of Crimes Act. The fact that you were acting under this general permission does not allow you to shoot. When you can do so depends on the law of private defence. If I were carrying a gun or spanner illegally I might be punished for it, but all the same I would use the weapon if I were being murderously attacked.

On principle you would be within your rights in doing so. The fact that your possession of the weapon is punishable under statute is no more relevant to a charge of assault or manslaughter than would be the fact that you have stolen it.

Such is the logic of the matter, but there is no indication that the courts accept it. In Shannon a question was made at the trial whether or not the defendant was carrying the scissors when he was attacked, and the trial judge did not warn the jury that the question was irrelevant; nor did the Court of Appeal suggest that the judge should have done so. When the defendant has armed himself against attack, and particularly when he has armed himself illegally, this is quite likely to be a circumstance of prejudice against him; he will not be looked upon so benignly as the defendant who possessed himself of a weapon in the stress of the moment.

The older authorities try to clarify the law of private defence by declaring that extreme force (otherwise called "deadly force," that is, force involving the intentional or reckless infliction of death or serious injury) may be used to avoid extreme harm, but not otherwise. "Extreme harm" included death or serious injury but might also include other serious harms like rape. The modem authorities, however, leave the rule of "reasonable relationship" at large, at least in the case of defence of the person.

This abandonment of the relative precision of the old law seems unfortunate, for reasons already sufficiently stated in connection with section 3 of the Criminal Law Act. If the proportionality rule survives the decision in Shannon, would it not at least be desirable, for the sake of protecting defendants from the vagaries not only of juries but (one must add) of judges, and from gusts of public opinion, that certain fixed rules should be laid down beforehand as to the occasions on which extreme force can be used for self-preservation? The list need not be exhaustive, for the rule could be that extreme but necessary force can be used in specified cases (a), (b), etc., "and in all other cases where such force would not be regarded by any reasonable person as disproportionate to the threat." Such a rule would have protected Shannon from an unjust conviction better than the rule stated by the Court of Appeal.


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