Self-defence is just defending yourself, another or property, whereas the statutory defence deals with prevention of crime. These are two separate defences. The two overlap and are essentially the same but should be treated separately.
This topic is sometimes called public and private defence. This is because the common law defence of self-defence is extended and, to some extent superseded, by the statutory defence of public defence (prevention of crime) under the Criminal Law Act 1967, s3
Definition: Where the D argues that it was necessary to use reasonable and proportionate force to defending himself, his family or his property or to prevent a crime.
Criminal Law Act 1967, s3
This section provides:
‘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.’
The necessity of force
Gladstone Williams (1987), where a man saw a woman become the victim of a robbery by a youth. This man struggled with the robber with a view to stopping him and handing him to the police. At this point the defendant appeared and took the view that the man was attacking the youth and stepped in to protect the youth. The defendant was successful in pleading prevention of crime, even though he was mistaken as to the actual facts. His defence is based on what he genuinely believed was happening.
Bird (1985): D told her ex boyfriend (v) at a party to leave after they had a bad argument. The V later came back and argued a second time with the D. The D poured pernod on him and the V slapped her across the face and pinned her to the wall. D smashed the pernod glass into his face. The court decided that it was unnecessary to show an unwillingness to fight and there were circumstances where a defendant might reasonably react immediately and without first retreating, as in this case. Force can be necessary in anticipation of unlawful violence.
AG ref (No 2 of 1983) 1984, D’s property was in the middle of a riot area. D made preparations to defend his property by making petrol bombs, as the further threats of attacks were imminent. It was held that there was a necessity to prepare for the use of force in this manner. D can anticipate violence and strike first.
The reasonableness of force
Palmer 1971: Where the attack on the D is over and no sort of threat remains any force used will be classed as unreasonable and therefore excessive, it will be classed as revenge. However, if the force is necessary then the jury must look at this from point of view of the D as the jury must consider instinctive reactions to reasonable even if in the light of day the force is unreasonable.
Criminal Justice & Immigration 2008 Act. Section 76 (6) makes it clear that the degree of force used by a person is not to be regarded as having been reasonable in the circumstances as he believed them to be if it was disproportionate in those circumstances.
Martin 2002: As the D used lethal force as the burglars were retreating from the house force used was excessive in the circumstances.
Mistaken belief and proportionality of force
Beckford 1988 it was held that a genuine but mistaken belief as to the V about to shoot the D, to which the D shot and killed the V, was not excessive force. Lord Griffiths said:
"A genuine belief in a fact which if true would justify self defence must be a defence to a crime of personal violence because the belief negates the intent to act unlawfully"
Voluntary intoxicated mistake not allowed for self defence
Section 76(5) of the Criminal Justice and Immigration Act 2008. The act makes it clear that "D cannot rely on any mistaken belief attributable to intoxication that was voluntarily induced".
Hatton 2005: D drank 20 pints of beer and thought V hit him with long stick. V was found dead with blows from sledgehammer. D was not allowed to use the mistaken belief as to V using force when claiming self defence and was found guilty of murder.
O’Grady 1987, where D was found G of manslaughter after mistakenly using excessive force against friend. As he had been drinking voluntarily the self defence and his mistake as to the use of force could not be allowed as evidence put to the jury.