In principle, the notion of self-defence is straightforward. A person is entitled to use reasonable force to defend themselves against attack and in certain other circumstances. Self-defence is a valid defence against prosecution when the circumstances warrant.

Guidance on the use of reasonable force states that, ‘a person may use such force as is reasonable in the circumstances’ for the purposes of:

  • self-defence; or
  • defence of another; or
  • defence of property; or
  • prevention of crime; or
  • lawful arrest.

In assessing the reasonableness of the force used, prosecutors should ask two questions:

  • was the use of force justified in the circumstances? – i.e. was there a need for any force at all? and
  • was the force used excessive in the circumstances?

The defence of self-defence rests on the belief of the person who is subjected to the assault. Recently, the House of Lords considered the issue of the justification of a claim of self-defence in civil, as opposed to criminal, proceedings.

The case arose after a man was killed by a firearms officer serving with Sussex Police. The police officer stood trial for murder and successfully pleaded self-defence on the basis that he honestly and reasonably (albeit mistakenly) believed that the man he shot posed a threat to him and to the public. He was acquitted.

However, the victim’s family pursued a civil case against the officer. This went to the House of Lords, which took the view that the civil law of tort exists to ensure that the rights of people are protected. One of those rights is the right not to be subjected to physical harm. This right has to be balanced by a person’s right to protect themself. At issue is the appropriate balance between these rights under civil law. The Lords ruled that for the purposes of civil law, to hold that a mistaken belief that one was about to be attacked could justify a pre-emptive attack in self-defence was a completely inappropriate striking of the balance of rights.

Accordingly, the defence against a civil suit on the basis of a mistaken belief must fail. The acquittal on the criminal charges did not mean that the policeman had not unlawfully assaulted the man.

On a split decision, the Lords ruled that the man’s family was free to pursue a claim for compensation from Sussex Police.