Anti-monarchy campaigners have called for reassurances from the police that peaceful protests on the day of the royal wedding will not be obstructed.

The Republic pressure group has written to the head of Thames Valley Police ahead of Prince Harry and Meghan Markle’s big day.

Graham Smith, chief executive of Republic, asked Chief Constable Francis Habgood to confirm that those carrying placards or banners will not be arrested, unless there is a genuine risk to public safety.

Mr Smith said in his email: “The monarchy is a contested institution and, while this is a private wedding, all major royal events such as this are used as PR for the monarchy.

“It is therefore vital that the usual procedures and policies for allowing and facilitating peaceful protest remain in place.”

He asked that peaceful protests would not be restricted within the secure area and near the route of Harry and Ms Markle’s royal carriage procession. “Your assurance that a royal wedding is no grounds for banning peaceful protest will be welcomed, not just by protesters or republicans, but by millions of people who believe the right to protest is a fundamental part of British life,” Mr Smith said.

Police will effectively create a ring of steel around Windsor Castle’s St George’s Chapel as part of a massive security operation. The May 19 wedding is one of the largest public events policed by Thames Valley and in the run-up more police will be seen on patrol in Windsor, from armed officers to those with dogs and even mounted police.

TVP told the Observer: “Thames Valley Police will be working closely with our partners to deliver a safe, secure and happy event for all. Everyone has a right to express their views peacefully, however anyone looking to disrupt the event will be dealt with in a robust yet proportionate manner.”