The head of an anti-monarchy group arrested ahead of a planned protest on Coronation Day has branded the detention of him and dozens of others a 'direct attack on our democracy'.Republic chief executive Graham Smith, who was released on Saturday night after nearly 16 hours in police custody, said officers should 'hang their heads in shame'.The Metropolitan Police confirmed that 52 people were arrested for affray, public order offences, breach of the peace and conspiracy to cause a public nuisance around the coronation.Mayor of London Sadiq Khan said he had demanded 'clarity' from the force’s leaders on the arrests.PA