The common law has developed a concept of reasonable self defence (sometimes referred to as private defence) and there is statutory law covering public defence, in relation to prevention of crime. There is overlap between the two but also distinction, self defence may be used against someone who is not actually committing a crime, for example if the perpetrator is insane.
Criminal Law Act 1967
A person may use such force as is reasonable in the circumstances in the prevention of crime, or in effecting or assisting in the lawful arrest of offenders or suspected offenders or of persons unlawfully at large.
Necessity of force
The first question to consider is whether the force was necessary and this a point decided by the jury. The general principle is that the use of force is not justified.
Use of force can be found necessary if it is seen to be so in the situation that exists or that the defendant believes exists.
Gladstone Williams (1987)
Defendant saw a man struggling with a youth who was calling for help and intervened. In fact, the man was affecting a lawful arrest of the youth.
Defendant found not guilty of assault. As the defendant honestly believed that he was preventing an unlawful assault his actions were justified and though he had misunderstood the situation.
Criminal Justice and Immigration Act 2008
If D claims to have held a particular belief as regards the existence of any circumstances-
S76(4)(a) the reasonableness or otherwise of that belief is relevant to the question whether D genuinely held it; but
S76(4)(b) if it is determined that D did genuinely hold it, D is entitled to rely on it for the purposes of subsection
(3), whether or not-
S76(4)(b)(i) it was mistaken, or
S76(4)(b)(ii) (if it was mistaken) the mistake was a reasonable one to have made.
The Criminal Justice and Immigration Act (CJIA) 2008 gives a statutory basis to the defence being effective for defendant’s who genuinely hold a mistaken belief. S5 of the Act sets out that this does not necessarily apply if the defendant is voluntarily intoxicated.
Pre emptive action
The defence can also apply to an imminent attack.
Defendant was at her 17th birthday party and the victim, her ex-boyfriend arrived with his new girlfriend. Defendant and victim argued and she asked him to leave. He did so but then later returned and the argument continued. Defendant threw a drink over him, he pinned her against a wall and she punched him in the face, causing the victim to lose his eye. Defendant claimed that she had forgotten that she had a glass in her hand, which had subsequently broken.
Defendant charged with wounding under S20 of the Offences Against Person Act 1861. Defendant argued self defence. Trial judge directed the jury that in order to rely on self defence, the defendant must demonstrate that she did not want to fight. Defendant convicted of S20 offence.
The conviction was quashed on appeal. It was held that there was no obligation to demonstrate an unwillingness to fight.
It seems that withdrawing or demonstrating an unwillingness to fight can be used as evidence that the defendant is acting reasonably and in self defence but there is no absolute obligation to retreat.
.. A man about to be attacked does not have to wait for his assailant to strike the first blow, or fire the first shot, circumstances may justify a pre-emptive strike....
Reasonableness of force
The jury must decide if the force used was reasonable.
. It is both good law and good sense that a man who is attacked may defend himself... he may do, but may only do what is reasonably necessary. But everything will depend upon the particular facts and circumstances... it may in some cases be only sensible and clearly possible to take some simple avoiding action. Some attacks may be serious and dangerous. Others may not be…..if an attack is serious so that it puts someone in immediate peril, then immediate defensive action may be necessary. If the moment is one of crisis for someone in immediate danger, he may have to avert the danger by some instant reaction. If the attack is over and no sort of peril remains, then the employment of force may be by way of revenge or punishment or by way of paying off an old score or may be pure aggression. There may be no longer any link with a necessity of defence...
Defendant was a soldier at a checkpoint and shot at a stolen car which came towards him at speed. Defendant killed the victim, a woman in the back seat, with his final shot. Evidence proved this shot had been fired once the car had passed the checkpoint, so there was no argument for self defence.
Defendant was convicted of murder and this was upheld on appeal.
Defendant shot intruders at his home, one died and the other was seriously injured. Defendant heard the intruders and feared they may be violent towards him.
Defendant’s appeal on the ground of self defence was rejected, as he was found to use unreasonable force. However, court did reduce the conviction to manslaughter on the basis of diminished responsibility as the defendant was suffering from a longstanding paranoid personality disorder.
Criminal Justice and Immigration Act 2008
.. [in deciding whether the force used is reasonable] the following considerations are to be taken into account (so far as relevant in the circumstances of the case)-
S76(7)(a) that a person acting for a legitimate purpose may not be able to weigh to a nicety the exact measure of any necessary action; and
S76(7)(b) that evidence of a person's having only done what the person honestly and instinctively thought was necessary for a legitimate purpose constitutes strong evidence that only reasonable action was taken by that person for that purpose.
This recognises that someone under attack is under stress and thereofore may not be able to reason as precisely as in other circumstances and that this should be taken into account.