The head of anti-monarchist campaign group Republic was arrested by police at a protest in Trafalgar Square before the Coronation of King Charles III on Saturday.
BBC reported that protesters at the venue, wearing t-shirts with “Not My King” written on them were being detained, including Republic’s Chief Executive Officer, Graham Smith.
Thousands of people gathered to watch the Coronation procession from Buckingham Palace to Westminster Abbey ahead of the ceremony.
During the Coronation ceremony, which was being broadcast in Trafalgar Square over loud speakers, hundreds of protesters booed the declarations of “God Save the King”.
Around 300 people gathered for a protest organised by Republic Cymru in Cardiff City Centre.
In Scotland, supporters of Scottish independence chanted anti-monarchy slogans on a march in Glasgow city centre, while a separate rally was held by the group Our Republic, which campaigns for an elected head of state.
Around 13 Just Stop Oil protesters were arrested on the Mall in London, with a large group from the climate change campaign group seen in handcuffs.
Just Stop Oil has said five demonstrators were also arrested at Downing Street.
A spokeswoman for the group said their plan was “only to display T-shirts and flags”, adding: “This is a dystopian nightmare.”
The Metropolitan Police confirmed several arrests were made at demonstrations in the capital.
The force said “lock-on devices” – which protesters can use to secure themselves to things like railings – had been seized.
Several campaign groups and human rights groups criticised the “incredibly alarming” detentions, describing them as “something you would expect to see in Moscow, not London”.
The publication revealed that on Wednesday, the police force said they would have an “extremely low threshold” for protests during coronation celebrations, adding that demonstrators should expect “swift action”.
“The reports of people being arrested for peacefully protesting the coronation are incredibly alarming”, said Human Rights Watch UK director, Yasmine Ahmed.
On Friday, Mr Smith said he had been speaking with the Met to organise the protest since January. He was not concerned he would be arrested, he said, as the new laws would not apply to their plans.
He told BBC Radio Leeds that Republic “certainly have no intention of actually disrupting” the proceedings.
“We will be very visible, we will be loud, we will be hard to miss, but the procession and the plans for the coronation will go ahead uninterrupted by us.”
Republic said on Saturday morning that hundreds of their placards had been seized and questioned: “Is this democracy?”
