Palestine Action's co-founder has won a legal challenge over the group's ban as a terrorist organisation on two grounds.
However, it will remain outlawed for now as the government intends to take the case to the Court of Appeal.
Huda Ammori launched the challenge after former home secretary Yvette Cooper's decision to proscribe the group, which came into force in July last year.
It followed action by members of the group that included breaking into RAF Brize Norton and spray-painting two aircraft.
The ban put Palestine Action on the same footing as ISIS and al Qaeda, making membership or support of a crime punishable by up to 14 years in prison.
Even wearing a T-shirt or carrying a sign with the group's name on it can carry a six-month sentence.
Ms Ammori called the ruling at London's High Court "a monumental victory both for our fundamental freedoms here in Britain and in the struggle for freedom for the Palestinian people".
She said the ban had resulted in nearly 3,000 unlawful arrests and claimed it "was always about appeasing pro-Israel lobby groups and weapons manufacturers, and nothing to do with terrorism".
Home Secretary Shabana Mahmood said she was "disappointed" and disagreed with the court that the ban was disproportionate.
She said she would appeal against the ruling, and the government had used a "rigorous and evidence-based decision-making process" when outlawing the group.
"The court has acknowledged that Palestine Action has carried out acts of terrorism, celebrated those who have taken part in those acts and promoted the use of violence," Ms Mahmood said in a statement.
She said the ban still allowed people to protest peacefully in support of Palestinians.
Ms Ammori's lawyers had argued the ban was unprecedented and compared Palestine Action - which she co-founded in 2020 - to the suffragettes.
In her ruling, Judge Dame Victoria Sharp agreed Palestine Action "promotes its political cause through criminality".
However, she said the ban was still disproportionate as it interfered with the Human Rights Act, specifically the freedom of expression and freedom of assembly.
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Legal expert Joshua Rozenberg said the court had decided a very small number of the group's members carried out acts amounting to "terrorism" and these hadn't reached a level that warranted a blanket ban.
The Metropolitan Police said the group remains banned, "which means expressing support is still a criminal offence".
A statement said the force would "continue to identify offences where support for Palestine Action is being expressed" but would "focus on gathering evidence... for enforcement at a later date, rather than making arrests at the time".
Some 2,787 people have been arrested since the ban came into force, according to the Defend Our Juries group, which organises protests against the ban.
Raza Husain KC, representing Ms Ammori, had told the court that "priests, teachers, pensioners, retired British Army officers" and an "81-year-old former magistrate" were among them.
Normal People author Sally Rooney also supported the challenge.
The writer said she might not be able to publish new books in the UK after saying she would donate earnings to the group.
Earlier this month, six Palestine Action activists were cleared over a 2024 break-in at an Israeli-linked defence firm's site in Bristol.
They were accused of spraying paint from fire extinguishers, using crowbars and hammers to break computer equipment and smashing up the disabled toilet.
However, they were found not guilty of charges including aggravated burglary and violent disorder, while the jury failed to reach verdicts on allegations of criminal damage.
(c) Sky News 2026: Palestine Action wins High Court challenge over government's terror ban
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