Thousands of people found by the high court to have been illegally detained for hours by police at a central London protest may sue Scotland Yard for false imprisonment.
The high court has ruled that the Metropolitan police had broken the law in the way it kettled up to 5,000 demonstrators at the G20 protests in April 2009.
The judges heard police used the tactic of mass detention against protesters that they accepted were peaceful, with officers meting out punches to the face, slaps and shield strikes as they tried to move a demonstration against climate change.
Judges found that the force used by police was "unjustified", criticised "imprecise" instructions given by senior officers about releasing innocent people, and said the mass detentions for five hours were an unlawful deprivation of liberty under article 5 of the European convention on human rights.