Campaign group Defend Our Juries said five of its spokespeople were arrested as it prepared to announce further mass protest against the ban on Palestine Action.
The organisation said more than 1,000 people will take action on September 6 in Parliament Square, holding signs saying “I oppose genocide. I support Palestine Action”.
This follows a number of demonstrations over the summer in which more than 700 people have been arrested and 114 charged.
On Tuesday, Defend Our Juries said supporters including Tim Crosland and law student Paddy Friend had been arrested by counter-terrorism police.
Mr Friend had reportedly hosted a Zoom call with other members to give legal advice to those planning to take part in the mass protest action.
A spokesperson for Defend Our Juries said: “This is scandalous. Locking up our key spokespeople just hours before they were due to hold a press conference announcing more peaceful Lift the Ban protests constitutes an unprecedented assault on free speech in our country.
“This level of political repression is not what we expect in a democracy – it’s the kind of tactic typically associated with authoritarian regimes around the world.
“Despite this dystopian crackdown targeting perceived organisers of peaceful protests, the mass action will go ahead, with 1,000 people pledging to hold signs.
“The mass defiance of the unjust ban on Palestine Action is unstoppable.
“The Home Office and the Met would have known about our press conference today.
“The counter-terrorism police are clearly targeting people they perceive as organisers, and the key spokespeople arrested were told they were being arrested for hosting public Zoom calls.
“No-one has been arrested for joining the Zoom calls, only the hosts, and we will be holding another Zoom call tonight ahead of our action on Saturday.”
The five were arrested under section 12 of the Terrorism Act, which covers support for banned groups.
Kerry Moscogiuri, director of campaigns and communications at Amnesty International UK, called the arrests “incredibly concerning” and said those held should be immediately released.
“The mass peaceful demonstrations they have organised over recent weeks are protected by international human rights law, and to think they run the risk of being imprisoned for up to 14 years is a terrifying example of the UK authorities’ willingness to use authoritarian practices to silence dissent,” she added.
The Metropolitan Police said that two men aged 26 and 55, and a 61-year-old woman, were arrested in London, while a 48-year-old woman was held in Kendal, Cumbria, and a 39-year-old man in Barnsley, South Yorkshire.
They were all arrested on suspicion of encouraging support for a proscribed organisation.
Chief Superintendent Helen Flanagan, head of operations for the Counter Terrorism Command, said: “These arrests have been made as part of an ongoing investigation into people we suspect have been involved in encouraging support for the proscribed group Palestine Action.
“We know there is a great strength of feeling towards the situation in Palestine and thousands have been able and continue to be able to express their views through protest and demonstrations, without breaking counter terrorism laws.
“But Palestine Action is clearly proscribed as a terrorist group, and those showing support for this particular group, or encouraging others to do so, can expect to be arrested, investigated and prosecuted.
“There are serious consequences for those who are found guilty of an offence under the Terrorism Act, so I would urge anyone considering showing public support towards this proscribed group to reconsider.”
On Tuesday Police Scotland said a 59-year-old man had been arrested in the Oban area and charged as part of an “investigation into those involved in encouraging support for Palestine Action”.
The force added: “He is due to appear at Oban Sheriff Court on Wednesday, September 3, and a report will be submitted to the procurator fiscal. Inquiries are ongoing.”
