Palestine Action will be banned from midnight after a judge refused its request to temporarily block the government from proscribing it as a terror group.
On Friday, a High Court judge refused the group more time to pursue legal action against the government’s decision.
It means supporting Palestine Action will become a criminal offence, with membership or expressing support for the direct action group punishable by up to 14 years in prison.
The group’s co-founder Huda Ammori said her lawyers will seek an “urgent appeal” to prevent what she called a “dystopian nightmare”.
Mr Justice Chamberlain said: “I have concluded that the harm which would ensue if interim relief is refused but the claim later succeeds is insufficient to outweigh the strong public interest in maintaining the order in force.”
The judge said they could apply for permission to appeal Friday’s decision at the Court of Appeal.
Shortly after on Friday evening, a hearing at the Court of Appeal to challenge the decision got under way.
The proposed ban, which amends the Terrorism Act 2000, will come into force after being approved by both the House of Commons and House of Lords earlier this week.
The move was taken to ban the group after an estimated £7m of damage was caused to planes at RAF Brize Norton last month, in action claimed by Palestine Action.
At a hearing earlier on Friday, Raza Husain KC, barrister for Palestine Action’s Ms Ammori, told the court banning the group would be “ill-considered” and an “authoritarian abuse” of power.
“This is the first time in our history that a direct action civil disobedience group, which does not advocate for violence, has been sought to be proscribed as terrorists,” he said.
In a 26-page judgement, Mr Justice Chamberlain said some of the consequences feared by Ms Ammori and others who gave evidence were “overstated”.
After the court’s ruling, Ms Ammori said “thousands of people across Britain wake up tomorrow to find they had been criminalised overnight for supporting a domestic protest group which sprays red paint on warplanes and disrupts Israel’s largest weapons manufacturer”.
She added: “We will not stop fighting to defend fundamental rights to free speech and protest in our country and to stand up for the rights of the Palestinian people.”
Around 81 organisations are already proscribed under the Terrorism Act 2000, including Hamas, al Qaida and National Action.
The Home Secretary Yvette Cooper announced plans to proscribe Palestine Action on 23 June, saying that the vandalism of the two planes was “disgraceful” and that the group had a “long history of unacceptable criminal damage”.
Mr Justice Chamberlain said an assessment on whether to ban the group had been made as early as March, and “preceded” the incident at RAF Brize Norton.
Four people have been charged in connection to the incident.