London police said Sunday that 532 people were arrested the previous day when supporters of a pro-Palestinian group recently outlawed as a terrorist organization intentionally broke the law to test the government’s ability to enforce the ban.

The Metropolitan Police Service released the updated figures as protesters demanding the immediate release of the remaining Israeli hostages in Gaza held their own march through central London on Sunday afternoon.

The vast majority of those detained on Saturday were arrested for displaying placards declaring their support for the group known as Palestine Action. Police updated their earlier totals and said 522 people were arrested for supporting a proscribed organization in violation of anti-terror laws. Another 10 people were arrested on a variety of charges, including assaulting and obstructing police officers.

Backers of Palestine Action staged the protest to underscore their belief that the government is illegally restricting freedom of expression by banning a direct action organization that has challenged its policies.

Home Secretary Yvette Cooper, who oversees law enforcement in Britain, rejected that characterization, saying Palestine Action was banned after committing serious attacks involving violence, significant injuries and extensive criminal damage.