A police ban on Extinction Rebellion protests in London last month was unlawful, High Court judges have ruled.
The Metropolitan Police imposed the ban, which prevented two or more people from the group taking part in protests, under the Public Order Act.
But judges have ruled that police had no power to do this because the law did not cover “separate assemblies”.
Activists say the police could now face claims for false imprisonment from “potentially hundreds” of protesters.
The Met said it would “carefully consider” the ruling.
The protests cost £24m to police and led to 1,828 arrests, with 165 people charged with offences, the Met says.
During the court hearing, the force had argued that the ban was the only way to tackle widespread disruption.
Announcing their judgement, however, Lord Justice Dingemans and Mr Justice Chamberlain ruled in favour of Extinction Rebellion.