A citizen’s arrest is when you, as someone who is not a police officer, detains a person because you know the other person is committing or has just committed an offence such as a theft, assault or criminal damage.
As soon as practicable after the arrest, you must arrange for the other person, and any property found on the other person, to be delivered into the custody of a police officer. You are legally required to inform the person why you have arrested them unless the suspect’s actions make it impractical to inform them.