The Power of Arrest in the UK

The power of the police to arrest someone can arise from the Common Law (in this context, that law which doesn't originate from an Act of Parliament) - for example, for 'breach of the peace'; or under specific legislation (a few "independent" powers remain - it is my understanding, though I can't confirm this - do you know? (if so drop me a line) - that arrest of deserters is one of them) - but most arrests are made - either

* under a warrant for arrest. This is signed by a Justice of the Peace (also known as a 'magistrate' - the terms are interrchangeable). For more detailed information from the UK Ministry of Justice press here.

* under s24 of PACE [Full Title - The Police and Criminal Evidence Act 1984] - PACE s24. Note this section was amended by the Serious Organised Crime and Police Act 2005 ss. 110(1), 178; and S.I. 2005/3495, art. 2(1)(m) - the link above is to that version which is now in force.

s24 distinguishes between past, current and future events. The key safeguard is the "reasonable suspicion" that the arresting officer must have. You can debate how effective such a safeguard may be in different circumstances.

"Citizen's Arrests" are possible in the UK (which means, not only the ordinary citizen, but a non-police officer - such as a store detective). This is covered by s24A of PACE.