On Saturday, ahead of the retrial of six Palestine Action activists at Woolwich Crown Court and in response to a Metropolitan Police U-turn on a policy of arresting protesters, Defend Our Juries called a silent defiant action in Trafalgar Square, London, which ended in 523 arrests on suspicion of showing support for a proscribed terrorist organisation.

After the High Court ruling in February that the government proscription of Palestine Action had been unlawful on two grounds, the Metropolitan Police announced that they would collect evidence of any ‘support for a proscribed group’, but not carry out arrests until the legal issues and a government appeal had been resolved.

With more than 2000 people already facing court for offences under Section 13 of the Terrorism Act, and with the possibility of civil action against the police should arrests be later deemed unlawful, this seemed like a sensible decision.

Defend Our Juries wrote to Sir Mark Rowley, the Met Commissioner, on Friday with a legal warning that arrests may be unlawful, even to the extent that individual officers could fall foul of the International Criminal Court Act 2001.

Among those arrested were anti-war campaigner Angie Zelter, environmentalist Sir Jonathon Porritt, and Massive Attack band member Rob Del Naja. Police were called in from all around the country in huge numbers, and a giant marquee was set up in nearby St James’ Square to process arrestees.

The government appeal on proscription is due to be heard at the end of the month, but a ruling is unlikely before the summer.