The head of an anti-monarchy group who was arrested before a protest at King Charles III’s coronation has been released from police custody, the group said.

Republic, which wants an elected head of state, said late on Saturday that its chief executive Graham Smith was released, some 16 hours after he was first detained.

He was one of more than 50 people held using new powers rushed into law this week by the UK government to crack down on protests by direct action groups.

London’s Metropolitan Police has been criticised for making the arrests, which included volunteers of a local women’s safety team that the force supports.

Last month, the Daily Mail newspaper claimed that protesters were planning to throw rape alarms to spook horses taking part in the parade, which included military bands.

The newspaper also said climate change activists from the Just Stop Oil group were planning to disrupt the event.

Just Stop Oil members were among those picked up on Saturday.

Republic’s Smith, who last week told reporters he and other members had no plans to disrupt the procession. The protest went ahead, with opponents waving “Not My King” placards and booing.

“Make no mistake. There is no longer a right to peaceful protest in the UK,” Smith tweeted.

“I have been told many times the monarch is there to defend our freedoms. Now our freedoms are under attack in his name.”

Human rights groups likened the arrests to those in authoritarian states but police defended their tactics, claiming it was “proportionate… in line with relevant legislation” after public concern.

London has been repeatedly targeted in recent years by direct action groups.

Hardline interior minister Suella Braverman promised police more powers to stop protesters using “guerilla tactics”.