Almost 140 people were arrested outside the US embassy in London on Saturday at the largest mass demonstration against the ban on Palestine Action since Andy Burnham became prime minister, according to the Metropolitan police.

Hundreds gathered in Battersea, south London, holding signs reading "I oppose genocide, I support Palestine Action". A vigil in support of the group was also held outside the US consulate in Edinburgh. The Metropolitan police said 139 people had been arrested.

Before the London gathering, the force warned that those taking part "face arrest as part of a robust policing operation", and that anyone "playing a key role in organising the event, giving instructions to others and/or providing logistical support" would probably be committing an offence.

What happened on the day

Demonstrators gathered through the afternoon, and police moved in to make arrests as the crowd stood outside the embassy. The Met said the operation was planned, that warnings had been issued in advance, and that the arrests followed the law as Parliament wrote it.

What the law says

Palestine Action was proscribed as a terrorist organisation under UK law in July last year, when Keir Starmer was prime minister. Supporting or displaying the group's symbols is a criminal offence, and police have used those powers repeatedly against demonstrators.

The Met said demonstrators were "meeting to purposefully commit a crime", framing the arrests as enforcement of the proscription rather than policing of a peaceful protest. Campaigners argue the ban is a political decision that criminalises legitimate speech about Gaza.

Why this protest was bigger

The size of Saturday's gathering is the story. Previous demonstrations against the ban have been smaller and more scattered, but this one drew hundreds to a single location and produced the largest number of arrests under Burnham's premiership, according to the Guardian.

That puts the new government in an awkward position. Burnham has taken a different tone on Israel and Gaza from his predecessor, and his government has faced pressure from both sides: from campaigners who want the ban reversed, and from those who argue the proscription is necessary.

The Guardian reports that the Met described the gathering as the largest such demonstration under Burnham's premiership, and the force's public statements framed the arrests as enforcement of the proscription rather than crowd control.

Why the numbers matter

The 139 arrests are the largest number at any single demonstration against the ban since Burnham took office, which is why the event travelled beyond the usual activist channels. Each arrest also creates a potential legal challenge, and civil liberties groups are already collecting accounts from those held.

The court case this week

The protest comes days before a Supreme Court appeal on Wednesday challenging the group's proscription. That hearing will decide whether the ban is lawful, and it gives the demonstrations a specific target and a deadline.

For the organisers, the timing is deliberate: maximum visibility before the highest court considers the case. For the police, the timing is a problem, because every arrest creates a potential legal challenge and a political argument about proportionality.

What the appeal will decide

Wednesday's hearing will not be about whether the demonstration was peaceful. It will be about whether the proscription itself is lawful, and that is a different question with a different answer. If the court upholds the ban, the policing approach seen on Saturday becomes the template for every future protest. If it strikes the ban down, the 139 arrests become evidence in a wider argument about how the law was used.

The policing question

The Met's approach has been to warn first and arrest those it considers organisers or active participants. That distinction is contested. Legal observers and civil liberties groups argue that arresting people for holding signs or attending a vigil amounts to policing opinion rather than conduct.

The force says it is applying the law as Parliament wrote it. The courts will ultimately decide whether the proscription itself is compatible with the right to protest, which is the question at the centre of Wednesday's appeal.

The political calculation

For Burnham, the demonstration creates a dilemma he did not choose. Reversing the ban would anger parts of the electorate that support it; keeping it invites accusations that his government is policing speech. Waiting for the court is the path of least resistance, and it is the one his office has taken so far.

What happens next

The immediate next steps are the court hearing and the processing of the 139 arrests. Beyond that, the political question is whether the government revisits the ban. Burnham has not said he will, and the Supreme Court case gives him a reason to wait for a ruling before deciding.

For readers following the UK and protest threads, our coverage of UK employment tribunal time limits covers how legal deadlines shape rights claims, the Canada-EU alliance shows how Western governments are repositioning amid the wider conflict, and the Obama-Trump arts rally is a reminder of how quickly symbolic politics becomes street politics.

The confirmed facts are the number of arrests, the location, the Met's warnings and the scheduled Supreme Court appeal. Whether the ban survives that appeal is unknown.