Arrests have begun at the largest demonstration yet opposing the proscription of Palestine Action.

More than 1,000 people had pledged to risk arrest on Saturday at a fresh protest in London against the ban, about double the number who took part in a demonstration last month at which 532 people were arrested. Participants gathered in Parliament Square by 1pm, many holding signs that read: “I oppose genocide. I support Palestine Action.” Defend Our Juries, who organised the demonstrations, said there were 1,500 sign-holders.

At 1.14pm, the Metropolitan police said: “Officers have begun making arrests for expressing support for proscribed terror organisation Palestine Action at the protest organised by Defend Our Juries.” Officers faced chants of “shame of you” when taking two elderly people using mobility scooters into police vans.

By 4pm, most of those participating in the main action remained on the square’s green. The Met claimed there had “been a coordinated effort to prevent officers carrying out their duties which has included physical and verbal abuse”, adding that a number of arrests were made for assault.

Defend Our Juries responded to the police’s claim, saying officers “violently [assaulted] peaceful protesters including the elderly, in order to try and arrest over 1,000 people for holding cardboard signs” and shared a video of officers shoving people to the ground.

A spokesperson for Defend Our Juries said: “State repression has not worked. We can confirm around 1,500 people are currently defying the ban in Parliament Square, with actions about to start in Scotland and Northern Ireland.

“This is becoming Labour’s poll tax moment. The resistance to this ridiculous ban keeps on growing exponentially. It is also bringing together social movements in common cause.”

Steve Masters, 55, was among those taking part. “I’m here because I oppose genocide and I also oppose the government’s overreach in proscribing Palestine Action,” he said. “They’ve lowered the bar of what terrorism is and almost made it meaningless.”

Steve Masters at the protest on Saturday. ‘While unpleasant, destruction of property to most people is not terrorism,’ he said. Photograph: Supplied

He served in the RAF as an aircraft technician for 19 years and took part in the protest while wearing his four service medals. “As somebody who was in the air force, attacking an air force jet is not something that I would do,” he said. “While unpleasant, destruction of property to most people is not terrorism. They’re not going out to explicitly harm people. It’s a travesty of justice.”

Protesters who signed up for Saturday’s demonstration were instructed to withhold their details from officers to force en-masse processing at police stations, which organisers said would make it “practically impossible” to arrest everyone.

Masters said he planned to withhold his details, meaning he would need to be transported and processed in a police station to complete his arrest. He said officers were in a “difficult position and I don’t envy them, but I also don’t have any sympathy for them either. They could stand there and say no. It takes moral courage because they may lose their jobs, but where is the red line?”

Judith Gradwell, 80, who also held a sign that read, “I oppose genocide. I support Palestine Action”, is unafraid of being arrested. “It doesn’t matter, I’ve got my sandwiches in my backpack,” she said.

Gradwell also plans on withholding her details from officers. She called the government’s decision to ban Palestine Action “ridiculous”, adding: “You would think after the Iraq war that they’d listen a bit more to what people on the streets were saying.”

In the 1970s, she protested against the Vietnam war outside the US embassy in London. “I thought the world would be a better place by now but it isn’t,” she said. “It’s a much worse place.”

Judith Gradwell, 80, called the ban on Palestine Action ‘ridiculous’. Photograph: Sammy Gecsoyler/The Guardian

Anne Karpf was in Parliament Square to support those taking part. “I think it’s very moving and, if I didn’t have caring responsibilities, I’d be in there holding a sign myself,” she said, standing under a banner that said “Holocaust survivor descendants against Gaza genocide”.

Karpf said her mother was a survivor of Auschwitz and her father was a survivor of Russian labour camps. “What they would be thinking, seeing what is happening now and being done in their name. I feel pretty certain that they would be horrified,” she said.

She called the proscription of the group “wrong on every single front” and an “outrageous curtailment of civil liberties”.

Anne Karpf (third from left) called the proscription of the group an ‘outrageous curtailment of civil liberties’. Photograph: Sammy Gecsoyler/The Guardian

Amnesty International said the arrests showed that “something is going very wrong here in the UK”.

Kerry Moscogiuri, director of campaigns for the organisation, said: “Let’s be clear, it is disproportionate to the point of absurdity to treat people sitting peacefully in a group holding signs in support of Palestine Action as ‘terrorists’. Any restriction on the rights to freedom of expression and peaceful assembly must be lawful, necessary and proportionate to achieving a legitimate aim.

“Criminalising speech in this context is only permitted when it incites violence or advocates hatred. Expressing support for Palestine Action does not, in itself, meet this threshold.”

Mike Higgins, 62, a blind man who uses a wheelchair, whose arrest was seen by millions on social media, also returned. He was arrested at the demonstration last month, which he said “starkly highlights what an absolute waste of time” the proscription of Palestine Action was for the state, taxpayers, police resources and, “most importantly, [for] Palestine and defending the people of Palestine, because that’s actually what this is really about”.

Mike Higgins, 62, a blind man who uses a wheelchair, whose arrest was seen by millions on social media, also returned to protest again. Photograph: James Manning/PA

Saturday’s demonstration has been the busiest by far. Hundreds of supporters gathered in Parliament Square and the anti-abortion group March for Life, set up a stage nearby with a sound system that occasionally blasted out music.

Near the start of the demonstration, several people fell over in a crush while water was thrown at officers, with the most frantic scenes unfolding on the western side of the park.

The protest was due to coincide with a march in London organised by the Palestine Solidarity Campaign and others, but also comes amid mounting controversy over this year’s DSEI arms fair, Britain’s flagship defence show, which is scheduled to open on Tuesday.

On Tuesday, hours before a press conference was due to start, Tim Crosland, a former government lawyer and one of the co-founders of Defend Our Juries, the group that has organised the demonstrations, was arrested by police.

On Thursday, six people who are alleged to be members of Defend Our Juries, or working closely with it, appeared at Westminster magistrates court to deny terror offences after they were accused of attempting to organise mass gatherings with the aim of rendering the ban on Palestine Action unenforceable.

The group said on Friday that it had sent a letter to Met commissioner, Mark Rowley, before the protest. It said police forces in Edinburgh, Totnes, Derry and Kendall had all decided not to arrest sign-holders.