Speaking for Republic, Graham Smith said today: "This is a first, an anti-monarchy protest inside Buckingham Palace. A fantastic statement of intent, citizens standing up in the home of the monarchy to declare their opposition to hereditary power.
"Charles is not an untouchable monarch, he is not immune to criticism and doesn't enjoy the deference that protected the monarchy while his mother was on the throne.
"Charles is not a unifying figure, he is a hypocrite on the environment, he has questions to answer about cash for honours and dodgy donations from Qataris and he is out of touch the concerns of ordinary people struggling with the cost of living crisis.
"I'm proud of our local activists who came together today to take this stand. Our local campaigns are expanding rapidly, with more than thirty now active around the UK.
Anti-monarchy protesters demonstrating n Trafalgar Square in London ahead of the coronation of King Charles III and Queen Camilla
"Republic will continue to protest against the monarchy up and down the country, with the next protest set for the state opening of parliament on November 7."
The group are calling for the monarchy to be replaced with an elected head of state.
On their website, Republic outlined why they wanted to see the monarchy abolished: "It's simple: Hereditary public office goes against every democratic principle.
"And because we can’t hold the King and his family to account at the ballot box, there’s nothing to stop them abusing their privilege, misusing their influence or simply wasting our money."