A private citizen has certain common law powers of arrest, but they must be exercised with care as wrongful arrest can result in a claim for damages.
The crime must be a serious one and not merely a breach of the peace, and he must be certain that an offence has been committed by, for example, witnessing it or being the victim.
Reasonable force may be used if the arrested person resists and he must be handed over to the police as soon as possible.
It is very rare for a person to be confronted by an intruder in their home.
In the heat of the moment it is not expected that you should make fine judgements as to how far you can go. You may take such steps which you honestly and instinctively believe are lawful and necessary self defence of either yourself, your family, or your property. You do not have to be attacked first to be able to use reasonable force in self defence.
Even if the intruder dies, provided you have used reasonable force in the circumstances described then you will not necessarily be prosecuted. If, having disabled the intruder you then go on and inflict further punishment then this would be deemed to be excessive and gratuitous force and you could be prosecuted.
If you suspect that a person is going to break into your house and you set a trap, rather than involve the police then this would not be deemed to be self defence or reasonable force.
If the intruder escapes with some of your property or you chase after them to affect a citizen's arrest you are still allowed to use reasonable force. The degree of force in this instance may have considerably reduced. To go beyond this as a form of punishment would again make you liable to a prosecution for assault and possibly civil action.
It should be understood that the Police will always have a duty to investigate this type of incident, but the Police and Crown office will always objectively assess all the facts recognising in the first instance that the intruder caused the situation to arise in the first place.
