Police detain 325 people at pro-Palestine Action protest at US embassy in London

Arrests come ahead of Wednesday’s supreme court challenge to the ban on the direct action group

Police have said they arrested 325 people on Saturday at a demonstration outside the US embassy in London against the proscription of Palestine Action.

In updated arrest figures released on Sunday, the Metropolitan police said 320 people were detained outside the building in Battersea, south London, for allegedly expressing support for an organisation banned under the Terrorism Act.

The arrests came ahead of Wednesday’s supreme court challenge to the ban on Palestine Action – the first direct action group to be proscribed under the Terrorism Act – which came into effect on 5 July last year.

Defend Our Juries, which has organised the mass civil disobedience campaign against proscription, said Saturday’s detentions took the total number of people arrested for allegedly supporting Palestine Action since the ban to 4,200. Most arrests have been for holding placards reading “I oppose genocide, I support Palestine Action.”

The overall number of detentions will probably feature in the hearing before the UK’s highest court, which was granted on the basis that it was arguable that the ban represents a disproportionate interference with the rights of freedom of speech and protest.

However, neither the high court, which ruled that the ban was unlawful, nor the court of appeal, which overturned the high court’s decision, gave much weight to the fate of the placard-holders.

About 2,500 of those arrested for alleged support of Palestine Action have been charged under the Terrorism Act but all trials have been postponed pending a definitive decision on whether or not the ban was lawful.

Saturday’s demonstrations – there was also a vigil in Edinburgh, although Police Scotland made no arrests – were the largest, against the ban, of Andy Burnham’s premiership.

In September, when quizzed by LBC radio’s Andrew Marr about the “elderly people, vicars and grannies” who have been arrested for holding placards allegedly supporting Palestine Action, the foreign secretary, Ed Miliband, said: “I don’t think anyone’s intent was to have those people criminalised. But obviously the supreme court has got to look at this issue and obviously it’s something we keep looking at as a government.”

The following week, in an interview with The Rest is Politics podcast, Shabana Mahmood said it had been “very uncomfortable” to see some protesters arrested for alleged support of Palestine Action. Mahmood, the home secretary, nevertheless defended the ban.

The supreme court hearing will conclude on Thursday, with judgment reserved until a later date.