The Supreme Court was concerned with Article 5 of the European Convention on Human Rights (ECHR). Article 5 specifies the situations in which an individual may be deprived of liberty - see Article 5(1) and also note Article 5(3). In particular, Article 5(1)(c) states:
"the lawful arrest or detention of a person effected for the purpose of bringing him before the competent legal authority on reasonable suspicion of having committed an offence or when it is reasonably considered necessary to prevent his committing an offence or fleeing after having done so;"
For the purposes of the European Convention, a breach of the peace is considered to be an "offence" even though it is not classified as an offence under English law.
This previous post (20th July 2012) noted the judgment of the Divisional Court - R (Hicks and others) v Commissioner of Police of the Metropolis  EWHC 1947 (Admin). This was a comprehensive judgment in which all the claims against the Police were dismissed. The Divisional Court held that the arrests and detention of each of the appellants prior to the wedding and up to its conclusion were lawful.
In 2013, the European Court of Human Rights Fifth Section gave judgment in Ostendorf v Germany - application 15598/08 in which the court examined Article 5 of the Convention.
Questions of law relating to Article 5 of the European Convention on Human Rights were heard by the Court of Appeal - R (Hicks and others) v Commissioner of Police of the Metropolis  EWCA Civ 3 (Maurice Kay, Leveson and Aikens LJJ).
The Supreme Court heard a further appeal relating to Article 5 - Hicks and others v Commissioner of Police for the Metropolis  UKSC 9 (Lords Mance, Reed, Carnwath, Toulson and Dyson). The court unanimously found the Police action to have been lawful.
The outcome is that Article 5(1)(c) is interpreted as permitting the Police to detain for preventive purposes followed by early release before the matter can be heard in a court. "It would be perverse if the law was such that in order to be lawfully able to detain a person so as to prevent their imminent commission of an offence, the Police must harbour a purpose of continuing his detention, after the risk has passed, until such time as the person could be brought before a court with a view to being bound over to keep the peace in the future. This would lengthen the period of detention and place an unnecessary burden on police resources." The court read the phrase "for the purpose of bringing him before the competent legal authority" as being implicitly dependent on the cause of detention continuing long enough for the person to be brought before the court. Early release from detention for preventive purpose will not breach Article 5 if the lawfulness of the detention can subsequently be challenged and decided by a court.
Rightsinfo 15th February 2017