Four burglars enter, three burglars leave... Householder arrested for murder...

The Uk Government produced a leaflet in 2005 - "Householders and the use of force agains intruders.

What is 'reasonable force' and does the law protect you?

Anyone can use 'reasonable force' to protect themselves or others, or to carry out an arrest or to prevent a crime. You are not expected to make fine judgements over the level of force you use in the heat of the moment. So long as you only do what you honestly and instinctively believe is necessary in the heat of the moment, that would be the strongest evidence of you acting lawfully and in self-defence. This is still the case if you use something to hand as a weapon.
As a general rule, the more extreme the circumstances and the fear felt, the more force you can lawfully use in self-defence.

What if you chase intruders as they run off?

This situation is different as you are no longer acting in self-defence and so the same degree of force may not be reasonable. However, you are still allowed to use reasonable force to recover your property and make a citizen's arrest. You should consider your own safety and, for example, whether the police have been called. A rugby tackle or a single blow would probably be reasonable. Acting out of malice and revenge with the intent of inflicting punishment through injury or death would not.

Will the police believe the intruder rather than you?

The police weigh all the facts when investigating an incident. This includes the fact that the intruder caused the situation to arise in the first place. The police have a duty to investigate incidents involving a death or injury. Things are not always as they seem - for example, on occasions people pretend a burglary has taken place to cover up other crimes, such as a fight between drug dealers.

Do you have to wait to be attacked?

You do not have to wait to be attacked before defending yourself if you are in your own home and in fear for yourself or others. In those circumstances the law does not require you to wait to be attacked before using defensive force yourself.

What if the intruder dies?

If you have acted in reasonable self-defence, as described above, and the intruder dies, you will still have acted lawfully. Indeed, there have been several such cases where the householder has not been prosecuted.
However, if, for example:

• having knocked someone unconscious, you then decided to further hurt or kill them to punish them

or

• you know of an intended intruder and set a trap to hurt or to kill them rather than involve the police

then you would be acting with very excessive and gratuitous force and could be prosecuted.

How would the police and CPS handle the investigation?

In considering these cases Chief Constables and Director of Public Prosecutions (Head of the CPS) are determined that they must be investigated and reviewed as quickly and as sympathetically as possible. In some cases, for instance where the facts are very clear, or where less serious injuries are involved, the investigation will be concluded very quickly, without any real need for arrest. In more complicated cases, such as where a death or serious injury occurs, more detailed enquiries will be necessary. The police may need to conduct a forensic examination and/or obtain your account of events.
To ensure such cases are dealt with as swiftly and sympathetically as possible, the police and CPS take special measures, namely:

• an experienced investigator will oversee the case

and

• if it goes as far as CPS considering the evidence, the case will be prioritised to ensure a senior lawyer makes a quick decision

It is a fact that very few householders have ever been prosecuted for actions resulting from the use of force against intruders.