London's police have defended their actions on coronation day, after the arrest of the head of a UK anti-monarchy group and dozens of others.
The Met Police said its officers made 52 arrests as King Charles III was crowned on Saturday.
The alleged offences included disrupting public order and conspiracy to cause a public nuisance.
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Republic leader Graham Smith was among those, sparking harsh criticism from the group and others who argued the force was being too draconian with peaceful protesters.
The activists, who want to replace the King with an elected head of state, had been campaigning near the statue of King Charles I in Trafalgar Square, about a kilometre from Westminster Abbey and just south of the protest route.
The group, which said it had informed police of its plans to hold placards and chant "Not my King", earlier said it was expecting about 1500 to 2000 protesters but it was unclear how many turned out.
On Saturday morning (Saturday evening AEST) several of the group's members were stopped near Trafalgar Square and led to police vans.
"This morning, Graham Smith and five members of our team were arrested," the group tweeted on Saturday, saying police "won't say what for".
"Hundreds of placards were seized. Is this democracy?"
The Met Police alleged it seized "lock-on devices" in the arrest of four people in St Martin's Lane, near the square.
A controversial and widely criticised UK public order bill came into force earlier this week, following a series of incidents since the Queen's death in which anti-monarchists turning up at royal engagements to protest.
The new rules, signed into law by the King on Tuesday, just days before the coronation, empower the police to take stronger action against peaceful protesters.
Republic member Matt Turnbull, who was reportedly detained, said straps holding its protest placards were "misconstrued".
"To be honest we were never going to be allowed to be a visible force here - they knew we were coming, and they were going to find a way to stop this," he told the BBC.
The Met Police earlier said its tolerance for any disruption would be low, and that it would deal "robustly" with anyone trying to undermine the celebration.
Commander Karen Findlay acknowledged the concerns, but defended the force's actions.
"The coronation is a once-in-a-generation event and that is a key consideration in our assessment," she said, adding that police allowed a protest involving large numbers to go ahead.
She described a "significant police operation" based on claims protesters were set to disrupt the coronation procession.
Republic said the Home Office sent the group a letter and asked for it to be forwarded to members, an act it interpreted as "a passive/aggressive intimidation of a legitimate protest group".
Others managed to protest along the route, dressed in yellow and waving placards with slogans including "king parasite" and "abolish the monarchy".
Environmental activism group Just Stop Oil said about 20 of its supporters were arrested.
The group, which demands no new licenses for any fossil fuel projects in the UK, said that the protesters were arrested on The Mall outside Buckingham Palace and outside Downing Street.
It said the activists did not carry out disruptive action, and that they were only wearing "Just Stop Oil" T-shirts and holding flags with the slogan.
The group criticised the government for what it described as banning legitimate dissent.
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- Reported with CNN and Associated Press
