Within minutes, police began arresting the demonstrators, as bystanders chanted “Shame on you” and “Met Police, pick a side, justice or genocide.”

Supporters say the ban stifles free speech

The UN human rights chief has criticised the British government’s stance, saying the new law “misuses the gravity and impact of terrorism.”

The decision to designate Palestine Action as a terrorist group “raises serious concerns that counterterrorism laws are being applied to conduct that is not terrorist in nature, and risks hindering the legitimate exercise of fundamental freedoms across the UK,” Volker Türk warned.

He added that according to international standards, terrorist acts should be confined to crimes such as those intended to cause death or serious injury or the taking of hostages.

Huda Ammori, Palestine Action’s co-founder, has condemned the government’s decision to ban it as “catastrophic” for civil liberties, leading to a “much wider chilling effect on freedom of speech.”

The group has been supported by prominent cultural figures including bestselling Irish author Sally Rooney, who said she planned to use the proceeds of her work “to keep backing Palestine Action and direct action against genocide.”

Israel – founded in part as a refuge in the wake of the Holocaust, when some 6 million European Jews were murdered – vehemently denies it is committing genocide.

Britain’s government stressed that proscribing Palestine Action as a terrorist group does not affect other lawful groups – including pro-Palestinian or pro-Israel voices – campaigning or peacefully protesting.

About 20,000 people, by a police estimate, attended a separate pro-Palestinian march in London.