The protestors from the campaign group were seen in handcuffs on the Mall, as Police cordoned off the group.
It comes after a group of republicans also appeared to be arrested on Saturday morning.
Footage shared on Twitter appeared to show Graham Smith, chief executive of the anti-monarchy group Republic, being apprehended by police in St Martin’s Lane, Westminster.
A significant police operation is under way in central London.
We have made a number of arrests in the area of Carlton House Terrace.
The individuals have been held on suspicion of breaching the peace.
— Metropolitan Police (@metpoliceuk) May 6, 2023
Pictures seemed to show demonstrators in yellow “Not My King” T-shirts, including Mr Smith, having their details taken by officers.
After the apparent arrests, Republic activist Luke Whiting, 26, told the PA news agency: “Six Republic members have been arrested including the CEO as the demonstration was starting at the edge of Trafalgar Square.
“It is unclear why, potentially it is because one of them was carrying a megaphone.
“It is unclear exactly whether the police are using these new powers and whether they are misusing them to stop protest happening.”
A further three people were arrested in the area of Wellington Arch.
They were held on suspicion of possessing articles to cause criminal damage.
There will be further updates later today.
— Metropolitan Police (@metpoliceuk) May 6, 2023
In a statement on Twitter, the Metropolitan Police said: “A significant police operation is under way in central London.
“We have made a number of arrests in the area of Carlton House Terrace.
“The individuals have been held on suspicion of breaching the peace.
“Earlier today we arrested four people in the area of St Martin’s Lane.
“They were held on suspicion of conspiracy to cause public nuisance.
“We seized lock-on devices.
“A further three…
