Scotland Yard said it acted in a 'proportionate manner'.
Scotland Yard said those arrested had been held on suspicion of affray, public order offences, breach of the peace and conspiracy to cause a public nuisance around the Coronation.
Speaking to the BBC's Laura Kuennsberg, he criticised the government for "passing legislation to clamp down on protest that breached British traditions of civil liberties". The Conservative Party has "a lot to answer for", he added. Writing on Twitter on Saturday evening, Mr Smith from Republic said he had been released but others from the group were still being held.
Footage during the day showed several protesters wearing "Not My King" T-shirts being detained, including Mr Smith.Watch: Anti-monarchy protester Matt Turnbull arrested near Trafalgar Square
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