The Metropolitan Police has arrested 55 demonstrators in central London holding placards which express support for Palestine Action, as dozens were detained at similar protests across the country.
It is the third weekend in a row in which protests against the proscription of Palestine Action as a terror group have ended in mass arrests in the capital, after 42 were hauled away by police last weekend.
The force confirmed on Saturday it had started making arrests after demonstrators wrote the message “I oppose genocide, I support Palestine Action” on white placards and held the signs aloft before being surrounded by police officers at the Mahatma Gandhi statue in Parliament Square.
The Metropolitan Police said 55 people were arrested under Section 13 of the Terrorism Act 2000 for holding the signs in support of the banned group.
Some were carried away by officers, while others were led away in handcuffs. A small number of counter-protesters held up placards which said “there is no genocide but there are 50 hostages still captive”.
The Met said 70 people were arrested at similar demonstrations in Parliament Square over the past two weekends.
A further eight people taking part in a separate Palestine Coalition march were arrested for supporting a proscribed organisation, the Met said, along with one for a racially aggravated public order offence and one for breaching Public Order Act conditions.
Avon and Somerset Police confirmed it had arrested 17 people under the Terrorism Act and a number of placards were seized during a protest in Bristol.
“We will always aim to enable peaceful protest, however where criminal offences are committed, including those related to proscribed groups, we will intervene,” the force said.
Greater Manchester Police said 16 people were arrested on suspicion of support of a proscribed organisation, adding that they remained in custody for questioning.
In Truro, Cornwall, eight people were detained for holding the same signs, according to organisers Defend Our Juries.
Devon and Cornwall Police said in a statement that around 30 protesters were involved in a peaceful demonstration.
The force added: “A number of placards which were contrary to the law remained on display despite police advice.
“Eight people, two men and six women, were arrested on suspicion of offences under Section 13 of the Terrorism Act 2000. They remain in police custody.”
The coordinated action comes ahead of a High Court hearing on Monday in which the co-founder of Palestine Action, Huda Ammori, will ask for the green light to challenge the home secretary’s decision to ban the group under anti-terror laws.
Yvette Cooper announced plans to ban the organisation after two Voyager aircraft were damaged at RAF Brize Norton in Oxfordshire on 20 June, an incident claimed by Palestine Action, which police said caused about £7m worth of damage.
The ban means that membership of, or support for, the direct action group is now a criminal offence punishable by up to 14 years in prison under the Terrorism Act 2000.
A spokesperson for Defend Our Juries said: “Just a few weeks ago, being arrested under the Terrorism Act was the stuff of nightmares.
“Now it’s a badge of honour that people are wearing with pride – the mark of resistance to genocide and standing firm for our democratic freedoms.”
An increased police presence was planned in Westminster for the Defend Our Juries demo in Parliament Square, the separate large-scale march to Whitehall by the Palestine Coalition and a static counter-protest by Stop the Hate.
Ahead of the protests, deputy assistant commissioner Ade Adelekan warned his officers would be on alert over the use of chants similar to that of “death to the IDF” led by Bob Vylan at Glastonbury Festival.
He said: “This is also the first large-scale protest on this issue since Glastonbury Festival where offensive chanting led by an artist on one of the stages prompted a police investigation.
“Investigations are also underway, led by Met officers, following similar uses of the same chant in London.”
He went on: “At previous protests, the area between the main march and any counter-protest has seen the most heated exchanges. Officers will be particularly alert to conduct, including chanting, in this area and will be working with stewards to ensure crowds keep moving past this point,” he said.
“Where they become aware of behaviour that crosses the line from protest into criminality, they will intervene and take appropriate action.”
Mr Adelekan said those expressing support for Palestine Action “will likely be committing an offence and will very likely be arrested”.
He added: “I would urge those people to consider the seriousness of being arrested under the Terrorism Act and the very real long-term implications – from travel, to employment, to finances – that such an arrest is likely to have for their future.”
He said the best way for protesters to stay within the law is to avoid “threatening, abusive and insulting language” or any support for banned groups.
