More than 500 people have been arrested at the first mass demonstration opposing the proscription of Palestine Action since the group’s ban was ruled unlawful by the high court.

Hundreds of people gathered in Trafalgar Square in London and presented signs reading: “I oppose genocide. I support Palestine Action.” Hundreds of demonstrators sat on camping chairs and on the ground as they held up their placards on Saturday afternoon. The Metropolitan police said 523 people had been arrested by midnight, with their ages ranging from 18 to 87.

Some of those sitting down holding signs were dressed as the suffragettes and others wore masks bearing the face of Keir Starmer. Mike Higgins, a blind disabled man whose filmed arrests at previous demonstrations have caused outrage, also took part in the action.

At the top of the square, near the National Gallery, large banners were displayed reading: “Jurors deserve to hear the whole truth” and “Israel starves kids”.

Shortly after 1pm, officers began arresting people on the edges of the demonstration. Several individuals were seen being carried off by officers away from the demonstration. One elderly woman using two walking sticks was escorted by an officer away from the protest. One woman told officers as she was being carried away: “You could be on your way catching real criminals.”

The Met said as of 2.50pm, it had made 92 arrests. Defend Our Juries, who organised the demonstration, said: “The Met are choosing to make arrests despite the government’s ban on the group being ruled unlawful by the high court, and leading lawyers warning that any arrests would be unlawful.”

A spokesperson for the group described the arrests as “truly surreal”, adding: “An already absurdly authoritarian measure has now descended even further into farce ahead of the Court of Appeal hearing this month.”

Qesser Zuhrah, a former Palestine Action-affiliated prisoner who was on hunger strike for 48 days, said the “entire world” is against the ban. The UN human rights chief, Volker Türk, has previously condemned the group’s “chilling” proscription.

Zuhrah said: “As former prisoners and hunger strikers, one of the main reasons of today is to defeat the exact purpose of the state for locking us up for 15 months and to make sure that we are never in these streets again. That’s why were here fighting, showing them that despite everything they put us through, we never forsake our cause.

She added: “This British government is hellbent on establishing that the ones that create the weapons are not the terrorists but the ones that destroy the weapons are the terrorists, which is insane.

“We believe that the ones that create the weapons and use them to bomb children, mothers, women and men that only dream of freedom, they are the terrorists. The ones raging a regional genocide are the terrorists,” she said.

Kamran Ahmed, who was on hunger strike for more than 60 days, said: “I’m here to support righteous people taking righteous action against the government.”

Ally, 72, a sculptor taking part in the demonstration, called the group’s proscription “blatantly absurd”.

“We’re just fed up with it but we just keep going until they stop it,” she said. “It’s not just about Palestinian Action, so much about protest is being shut down now. It’s getting really scary about what this government is doing about free speech and the right to protest.

“The government hasn’t got support for this one. It’s a rather stupid proscription,” she added.

Andy Simons, 73, a retired British Library curator, was there to support those taking part. He wore a sign around his neck with an image of a man peering through prison bars. The sign read: “Free, free speech.”.

Simons said: “Free speech, as long as it’s not violent or anything like that, is something we should have.”

Shabana Mahmood was given permission to appeal against the high court’s decision. Initially, the Metropolitan police said it would immediately stop arresting people for such offences under the Terrorism Act but would gather evidence for potential future prosecutions.

But after the home secretary was given permission to appeal against the decision the force said it had “revised” its enforcement approach, describing the statement made immediately after the high court’s decision as an “interim position”.

In February, the high court said the government’s proscription of the direct action group was “disproportionate and unlawful” and that most of their activities had not reached the level, scale and persistence to be defined as terrorism.

Mahmood’s appeal to the high court is due to be heard on 28 and 29 April.

Before the demonstration, the Met commander Claire Smart said: “Those attending should be aware that showing support for a proscribed organisation is an offence under the Terrorism Act, and we will not hesitate to act where the law is broken.

“At previous events linked to this group we have seen coordinated attempts to disrupt police activity, including obstructing officers and, at times, verbal or physical abuse. Our officers are trained to deal with these situations proportionately and effectively, and we are confident we have the plans and resources in place to respond appropriately, including making arrests where necessary.”

In response, Defend Our Juries said on X: “More Met lies. There has not been a single instance of prosecution among our supporter base relating to ‘obstructing officers’ or ‘verbal or physical abuse’.

“Our actions are peaceful, dignified (from our side, at least) and completely nonviolent.”