Police on Saturday arrested protesters in London for supporting the pro-Palestinian, anti-Israel activist group Palestine Action, which was on Friday banned by the UK parliament under anti-terror laws.

“Officers are responding to a protest in support of Palestine Action in Parliament Square. The group is now proscribed, and expressing support for them is a criminal offense. Arrests are being made,” the Metropolitan Police wrote on X.

Campaign group Defend Our Juries said in a press release that a group of 27 people, including a priest and a number of health professionals, had been arrested for offenses under the Terrorism Act.

They were holding cardboard signs, saying: “I oppose genocide. I support Palestine Action,” added the campaign group. Israel has denied all accusations of genocide.

Police warned on Friday that expressing support for Palestine Action would be a criminal offense after the ban kicked in at midnight.

“This includes chanting, wearing clothing, or displaying articles such as flags, signs, or logos,” said the force.

A spokesperson for Defend Our Juries said: “We commend the Counter Terrorism police for their decisive action in protecting the people of London from some cardboard signs opposing the genocide in Gaza and expressing support for those taking action to prevent it.”

The terror designation cleared parliament on Thursday, with a court challenge by Huda Ammori, who helped found Palestine Action in 2020, to try to stop it from becoming law, failing on Friday.

Judge Martin Chamberlain ruled against Ammori’s bid to pause the ban, meaning the proscription of Palestine Action came into force Saturday.

Husain asked for a temporary pause until Monday pending an appeal, but Chamberlain refused, saying: “You are going to have to trouble the Court of Appeal tonight.”

Ammori said in a statement: “We are seeking an urgent appeal to try to prevent a dystopian nightmare of the government’s making.”

The government announced last week it would ban Palestine Action under the Terrorism Act 2000, days after activists from the group broke into a Royal Air Force base and damaged two planes in protest against what the group says is Britain’s support for Israel.

Two aircraft at the base were sprayed with red paint, causing an estimated £7 million ($9.55 million) in damage.

Four Palestine Action activists were remanded in custody on Thursday after appearing in court over the incident.

Palestine Action has condemned the terror designation as an attack on free speech.

Proscription would make it a crime to be a member of or to support the group, with a maximum sentence of 14 years in prison.