The police imposed the ban Oct. 14 for the last four days of Extinction Rebellion's two-week "Autumn Uprising," a campaign of civil disobedience in London intended to pressure the government into action on the climate crisis.

"Extinction Rebellion is delighted with the Court's decision," Tobias Garnett, a human rights lawyer in Extinction Rebellion's Legal Strategy team, said in an Extinction Rebellion press release. "It vindicates our belief that the Police's blanket ban on our protests was an unprecedented and unlawful infringement on the right to protest. Rather than wasting its time and money seeking to silence and criminalise those who are drawing its attention to the Climate and Ecological Emergency, we call on the Government to act now on the biggest threat to our planet."

The police had issued the ban under Section 14 of the Public Order Act of 1986, which grants them the power to impose restrictions on assemblies that "may result in serious public disorder." But the court ruled that the police had overstepped their authority by banning a series of protests as if they were a single assembly.

"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 Section 14 of the 1986 Act," Lord Justice Digemans said, according to CNN. "The XR 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 Section 14 of the 1986 Act."

Anyone who was arrested under the ban may now sue the London police for false imprisonment, The Guardian pointed out.

"It's a very expensive mistake for the Metropolitan police," Jules Carey, part of the legal team that brought the case, told The Guardian. "I'm sure most of them would want to start off with an apology for the ordeal that they experienced, but all of them could potentially be awarded several thousands of pounds depending on how long they were arrested for and whether force was used against them."

More than 1,800 people were arrested during the two-week protests, CNN reported, and 400 were arrested after the ban.

The judicial review of the police order was brought by Green Party Members Jenny Jones, Caroline Lucas and Ellie Chowns, Labour Members of Parliament Clive Lewis and David Drew, Labour activist Adam Allnutt and Guardian columnist George Monbiot.

Chowns, a Member of European Parliament who was arrested for remaining in Trafalgar Square after the ban was announced, applauded the ruling.

"I'm delighted with this judgement because this is about fundamental democratic rights. The right to assembly and public protest are cornerstones of a functioning democracy," she said in a video shared on her Twitter feed. "Now Extinction Rebellion protesters have been raising the alarm about the climate crisis. We need to listen to that alarm, not outlaw it."

Extinction Rebellion launched in the UK in late October of last year and has since spread worldwide. In the UK, the group has three demands: that the government declare a climate emergency, that it act to halt biodiversity loss and achieve carbon neutrality by 2025 and that it convene a Citizens' Assembly to guide its actions on the environment.

The group's London demonstrations in October cost the police $31 million, according to CNN. For comparison, the police spend £15 million (approximately $19 million) on their violent crime task force every year.

"After eight days of continual disruption we took the decision to bring an end to this particular protest, a decision which we believe was both reasonable and proportionate," Assistant Commissioner Nick Ephgrave said in a statement reported by CNN. "I want to be clear; we would not and cannot ban protest. The condition at the center of this ruling was specific to this particular protest, in the particular circumstances at the time."

In court, it was revealed that the police ban followed an online message from Extinction Rebellion urging protesters to adopt the "be water" tactics used by demonstrators in Hong Kong, BBC News reported.

"Be water, crowds split up into fast moving groups and pairs, that network via phones," the message said. "You gather at particular spots in large numbers, until the police response building then you move to a new disruptive site."

BBC home affairs correspondent Daniel Sandford said the ruling would make it hard for the police to control similar protests in the future:

Today's High Court ruling takes away from officers the ability to impose a city-wide ban of future protests, which means demonstrators wanting to be "like water" - where they split into fast-moving groups - will be difficult to control if they are trying to disrupt a whole city.

So police will have to deal with what is in front of them.

If a specific protest in a specific place gets out of hand they will be able to close it down, but it will have to be a decision made by an officer on the spot, and not by someone sitting in a police station worrying about what protests may happen the next day.