The arrest of two republicans with placards on Dam Square during the investiture of king Willem-Alexander was a mistake, Amsterdam mayor Eberhard van der Laan has said.

The arrest of Hans Maessen, of the Nieuw Republikieins Genootschap, and a student activist known as Joanna was ‘a clear error’ and a ‘serious affair’, the mayor said.

‘The right to demonstrate and freedom of speech are constitutional rights. If something goes wrong, it hurts all of us,’ Van der Laan said. Their arrests had been the result of a shift change and an inquiry is underway, he said.

Mistake

Police said shortly after the arrests that it had been a mistake and the pair were released three hours later. They were removed from the square shortly before the royal family appeared on the balcony of the palace, despite assurances that individual protests would be allowed.

Nevertheless, Van der Laan said the day had passed off peacefully, with 40% fewer arrests and 30% fewer ambulance call-outs than on a normal Queen’s Day.

The mayor was speaking before a ceremony to present medals to people who had been involved in making the day a success. These included the team of council workers charged with removing bikes from the area around the Nieuwe Kerk.