Extinction Rebellion have won a High Court challenge against a police ban on protests throughout London.
Hundreds of climate protesters were arrested for defying the ban, which was imposed by the Metropolitan Police last month.
Extinction Rebellion held 10 days of protests in October, which shut down key areas of Central London, including Westminster, The City and London City Airport.
The Metropolitan Police used section 14 of the Public Order Act to try and prevent demonstrations involving more than two people.
The act was initially used to restrict protesters to Trafalgar Square in Central London, but police widened its powers following "continued breaches" of the order that caused disruption to Londoners.
Extinction Rebellion's lawyers argued that the police's actions were beyond the powers of the act.
Announcing the judgment, Lord Justice Dingemans and Mr Justice Chamberlain said that London's police force did not have the power to put a ban in place, because the act used does not cover "separate assemblies".
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Lord Justice Dingemans said: "Separate gatherings, separated both in time and by many miles, even if coordinated under the umbrella of one body, are not a public assembly within the meaning of… the act.
"The XR 'autumn uprising' intended to be held from 14 to 19 October 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 did note, however, that there are powers within the Public Order Act that could be used to legally "control future protests which are deliberately designed to 'take police resources to breaking point'" – which is one of the stated aims of Extinction Rebellion.
Speaking outside the High Court, Tobias Garnett, a human rights lawyer working with the climate group, said he was "delighted" at the result.
Mr Garnett added: "It vindicates our belief that the police's blanket ban was an unprecedented and now unlawful infringement on our right to protest.
"It's a victory for those who want to draw the government's attention to what scientists have been telling us for decades."
The Metropolitan Police said that 1,832 people were arrested during the October protests, with more than 150 being charged with offences – it is not yet clear what will happen to those who were arrested under the act.
The Metropolitan Police did not initially respond to request for comment.