A legal observer "kettled" during a demonstration against Government cuts has won a High Court declaration that police acted unlawfully when they filmed her and required the handover of personal information before letting her go.
The Metropolitan Police argued they were legally entitled to obtain, and retain, the information for crime prevention purposes before allowing Susannah Mengesha to leave the kettle.
But Lord Justice Moses and Mr Justice Wyn Williams, sitting in London, ruled they had acted outside their powers.
Lord Justice Moses said: "The absence of any statutory power to obtain identification in the circumstances in this case establishes conclusively the unlawfulness of the police action in requiring (Ms Mengesha) to be filmed and give her name and address and date of birth before she was released from containment."
Ms Mengesha, a law graduate and caseworker at the Bar Pro Bono Unit, was corralled in a crowd of protesters for two hours on November 30 2011 at a trade union march against public sector pension cuts. Some of the crowd, including Ms Mengesha, were blocked in to a street during the march through the West End. Police said the containment was "necessitated by a reasonably apprehended imminent breach of the peace".
While the judges agreed that containment was necessary, they declared being filmed and having to give the police personal details as "the price of release" a step too far. Their ruling will be welcomed as important backing for the freedom to protest without the "chilling" effect of being forced to hand over particulars.
The judge declared: "It was not lawful for the police to maintain the containment for the purposes of obtaining identification , whether by questioning or filming. It follows that it was not lawful to require identification to be given and submission to filming as the price for release."
Ms Mengesha, who is now training to be solicitor, was allowed out of the kettle some two hours later at 5.52pm. The filming and taking of personal details occurred when the police assessed that containment was no longer necessary.
Ms Mengesha said some 100 detainees were searched for "offensive weapons or dangerous instruments" before their release - but were also told they had to give their personal details to obtain their freedom. She was "tagged" - filmed close up under bright lights - for identification purposes by a civilian employee of the police and gave her name, address and date of birth to a police officer, Pc Scott Penney.
A Metropolitan Police Service spokesman said later: "We are aware of the judgment today and will now give it our full consideration and take forward any learning."