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London police arrested 139 people on Saturday, October 31, as hundreds of protesters gathered outside the US Embassy in support of Palestine Action, the direct-action group banned in Britain under anti-terrorism law. Most of those arrested were detained for expressing support for a proscribed organisation, according to London's Metropolitan Police.
What happened outside the embassy
The demonstration was a lunchtime "mass action" organised by Defend Our Juries, with protesters holding placards reading "I oppose genocide, I support Palestine Action." According to reports from The Times of Israel and Al Jazeera, officers began detaining people shortly after the protest began, and the arrest total rose from 48 earlier in the day to 139 by the evening. Police said more arrests were expected while officers remained at the scene, and warned in advance that enforcement would extend beyond people personally carrying placards to organisers and anyone providing logistical help.
Commander Adam Slonecki, who led the operation, was quoted as saying that those attending knew supporting a proscribed organisation was unlawful and were "essentially meeting to purposefully commit a crime." Many of those protesting were retirees, and one protester climbed a tree outside the embassy waving a placard. A parallel vigil was held outside the US Consulate in Edinburgh, where no arrests were reported.
Why supporting the group is a crime in Britain
Palestine Action, founded in 2020, says it aims to stop what it calls genocide by disrupting what it describes as corporate enablers of the Israeli military-industrial complex — an accusation Israel strongly denies. The British government proscribed the group as a terrorist organisation in July 2025, putting it on the same banned list as groups such as al-Qaeda and ISIL. Under that ban, membership in or support for the group is a criminal offence punishable by up to 14 years in prison.
The scale of enforcement since then is striking. Organisers say more than 4,000 people have now been detained for defying the ban since July 2025. Home Office data cited in coverage put Palestine Action-linked arrests at 3,630 of 3,867 terrorism-related arrests in the year to June 2026 — about 94 percent of the total. Critics argue the ban criminalises peaceful protest; supporters of the ban argue the group's direct action crossed into terrorism. That argument is about to be tested at the highest level.
The Supreme Court appeal on November 4
Saturday's protest came just days before a Supreme Court appeal on Wednesday, November 4, challenging Palestine Action's designation as a terror group. It was also reported as the first major demonstration against the proscription since Prime Minister Andy Burnham took office in July. The United States sanctioned Palestine Action in August, designating it as a terror group there too.
Whatever the court decides on November 4, it will not retroactively undo Saturday's arrests — but it could reshape everything that follows. If the designation falls, the legal basis for arresting placard-holders falls with it. If it stands, Saturday's pattern — mass arrests at pre-announced, deliberately unlawful protests — is likely to repeat, with each round adding to a detention total that has already passed 4,000. The protesters outside the embassy on Saturday knew they would probably be arrested. That, for both sides, was the point.
For background on Britain's current political moment, see our earlier coverage of the prime minister's position on a formal slavery apology: UK Prime Minister Open to Formal Slavery Apology, but Rules Out Reparations.