Extinction Rebellion activists are launching legal action against the police over a London-wide ban on their protests.

The move comes amid growing criticism of the ban, made under public order legislation already used to restrict the action to Trafalgar Square.

Activists continued protests in the capital in defiance of the police order, targeting the Department for Transport and locking themselves to a caravan on Millbank, prompting more arrests.

Human rights lawyer Tobias Garnett, working for Extinction Rebellion, said the group would be filing a High Court claim challenging the ban on the grounds it is “disproportionate and unlawful”.

The group was planning to file a claim on Tuesday afternoon, and was seeking an expedited hearing.

On Tuesday evening, Mayor Sadiq Khan – who oversees the Metropolitan Police, said he had asked officers to find a way for those who wanted to protest to be able to do so legally and peacefully.

He said he had “received assurances that Extinction Rebellion are not banned from protesting in our city”, adding: “Neither I nor the Deputy Mayor for Policing and Crime was informed before the Metropolitan Police took the operational decision to impose a Section 14 order on Extinction Rebellion Autumn Uprising last night.

“I’ve met with senior officers today to seek further information on why they deemed this necessary.”

Extinction Rebellion co-founder Gail Bradbrook outside the Department for Transport in Westminster Credit: Extinction Rebellion handout/PA

Mr Garnett said the police order limiting protests “risks criminalising anyone who wants to protest in any way about the climate and ecological emergency that we face”.

Under the current order, any assembly – classed as a gathering of two or more people – linked to the Extinction Rebellion ‘Autumn Uprising’ in London is unlawful.

Lawyers have questioned the legality of ban, aimed at halting further protests after more than a week of disruption by the environmental activists in London, while a number of politicians expressed outrage over the move.

Responding to the ban, teenage climate activist Greta Thunberg tweeted: “If standing up against the climate and ecological breakdown and for humanity is against the rules then the rules must be broken.”

Anti-Brexit barrister Jo Maugham QC claimed the move was a “huge overreach” of police powers, human rights lawyer Adam Wagner called it “draconian and extremely heavy-handed”, and Allan Hogarth from Amnesty International said it was “unacceptable”.

Shadow Home Secretary Diane Abbott said: “This ban is completely contrary to Britain’s long-held traditions of policing by consent, freedom of speech, and the right to protest.”

Green Party MEP Ellie Chowns, who was arrested in Trafalgar Square, Green MP Caroline Lucas and shadow policing and crime minister Louise Haigh also spoke out against the move.

But Home Secretary Priti Patel backed the police in a tweet, saying: “Officers from around the country have done a fantastic job policing XR protests. Supporting our Police is vital.

“Labour support the law breakers who have disrupted the lives and businesses of Londoners. They cannot be trusted in Downing Street or the Home Office.”

Police moved in to clear Trafalgar Square on Monday evening, telling protesters to leave the site by 9pm or risk arrest.

On Tuesday, Metropolitan Police Deputy Assistant Commissioner Laurence Taylor said the protest ban was brought in after “continued breaches” of the condition limiting the demonstration to Trafalgar Square.

He said: “I want to be absolutely clear, the conditions put in place yesterday afternoon do not in any way ban protests from London, nor do they ban the activities of Extinction Rebellion as a group.

“These conditions specifically state that any assembly linked to Extinction Rebellion’s ‘Autumn Uprising’ must now cease.

“The decision to impose further conditions was made in order to help us get London moving again. It is a lawful decision which we felt is entirely proportionate and reasonable to impose after nine days of sustained, unlawful assembly and protest by Extinction Rebellion.”

The Met said that using Section 14 to limit the location and duration of protest action was “not unusual”.

Extinction Rebellion activists defied the order and on Tuesday morning, the group’s co-founder, Gail Bradbrook, was arrested after action to target the Department for Transport in Westminster over HS2 and airport expansion.

Police also dealt with a road block near Baker Street and told a number of protesters camped in Vauxhall Pleasure Gardens to move on or risk arrest.

Protesters locked themselves to a caravan parked by Millbank tower in central London, with police spending more than two hours trying to free them using electric saws.

The protest outside the MI5 headquarters aimed to highlight the issue of food security.

Extinction Rebellion protesters outside MI5 Headquarters on Millbank in London Credit: Aaron Chowen/PA

Ilya Fisher, a fine art photographer from Cornwall, said she was taking part despite never having been arrested before.

She said: “I’m doing this because I want other people to see ‘why is such a boring ordinary person doing this?’ and they will look into the climate science.

“The Government isn’t protecting us. If we wait until 2050 for the carbon emissions to be reduced it’s way too late.”

By Tuesday afternoon, police said 1,489 people had been arrested in connection with the “Autumn Uprising”.

And 92 people had been charged for offences including failing to comply with a condition imposed under Section 14 of the Public Order Act 1986, criminal damage, and obstruction of a highway.