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”.
Lawyers for the group described the police action as “hastily imposed and erratically applied”.
They say the Met Police now faces claims for false imprisonment from “potentially hundreds” of protesters.
Protests cost £24m to police and resulted in 1,828 arrests, with 165 charged with offences, the Met says.
During Wednesday’s 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.
Lord Justice Dingemans said: “Separate gatherings, separated both in time and by many miles, even if co-ordinated under the umbrella of one body, are not a public assembly within the meaning of… the Act.
“The XR [Extinction Rebellion] autumn uprising intended to be held from October 14 to 19 was not therefore a public assembly… therefore the decision to impose the condition was unlawful because there was no power to impose it under… the Act.”
The judges noted that there are powers within that act which may be used lawfully to “control future protests which are deliberately designed to ‘take police resources to breaking point”‘.
During 10 days of climate change protests starting on 7 October, activists shut down areas around Parliament and the Bank of England, and targeted London City Airport.
Police had tried to restrict them to Trafalgar Square, under Section 14 of the Public Order Act.
However, that ban was lifted four days later, with officers saying that it was no longer necessary because demonstrations had ended.
During the court hearing, Phillippa Kaufmann QC, for Extinction Rebellion, told court the police ban had been “wholly uncertain, an abuse of power and irrational”.
Responding to the ruling, Extinction Rebellion UK tweeted “we won’t be silenced”.
Green Party peer Jenny Jones described the legal win as “historic”.
Speaking outside the court, she said: “The police can over-step the mark. The police are getting more and more strong powers that they are misusing – and that’s absolutely unacceptable.”
Ms Lucas described the ruling as “brilliant news”.
Jules Carey, a solicitor representing protestors, said the ban had been “hastily imposed” and “erratically applied”.
He said: “The police have powers to impose conditions to manage protests but not to ban them.
“This judgement is a timely reminder to those in authority facing a climate of dissent – the right to protest is a long-standing fundamental right in a democratic society that should be guarded and not prohibited by overzealous policing.”