That led the pressure group Republic, which campaigns for the abolition of the monarchy and its replacement with an elected head of state, to seek reassurances from Thames Valley police that they would allow peaceful protests to take place. It said it did not want to see a repeat of what the arrests of people seeking to protest against the monarchy during the wedding of Prince William and Catherine Middleton, in April 2011.At one stage activists who were planning a mock execution of Prince Andrew to mark the wedding were detained. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Republic are not planning to organise protests themselves, as the event coincides with an international republican conference in central London, but Mr Smith this week wrote to Francis Habgood, the Chief Constable of Thames Valley Police, asking for police not to disrupt those that do take place. “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.”There were calls earlier this year for protests outside the wedding after it emerged that Simon Dudley, the Tory council leader in the Royal Borough of Windsor and Maidenhead, had urged police to clear the area of rough sleepers and beggars before the event. Prince Harry and his fiancee Meghan Markle arrive for a reception with delegates from the Commonwealth Youth Forum at the Queen Elizabeth II Conference Centre, London,Credit:Reuters/Pool That could include anti-Monarchist chanting, but only if it was seen as leading to friction and confrontations with sections of the huge pro-Monarchist crowd attending the event.The prospect of demonstrations has prompted condemnation, with royalists describing would-be protestors as “killjoys”.Tricia Wright, from Godalming, Surrey, wrote on Twitter: “Why would you want to protest at a couple’s wedding? Spiteful and totally unnecessary.” Graham Smith, of Republic, which campaigns for the abolition of the monarchyCredit:Christopher Pledger/The Telegraph Graham Smith, the chief executive of Republic, told the Daily Telegraph: “Senior officers implied at the time that royal events such as weddings should be kept special, but it’s not for the police to say one day should be out of bounds to protests.“In a democracy people should be able to protest against the head of state and its institutions or issues such as the treatment of the homeless.”He added: “The Monarchy cannot be off limits, especially if it is going to turn the wedding of one of its members into a huge PR stunt.” When Prince Harry and Meghan Markle marry in Windsor’s St George’s Chapel next month they can be sure of a warm reception from the thousands of people expected to line the streets outside.But they may also have to contend with less-than friendly chanting and placard waving after police yesterday gave the green light for protesters to stage demonstrations against the monarchy.Senior officers have indicated they will not arrest or attempt to remove anyone mounting protests in Windsor on May 19, unless their behaviour threatens to disrupt the event itself.It is anticipated that anti-monarchists groups could use the wedding – which will see the royal couple take a two mile carriage ride past the crowds outside Windsor Castle – as a high-profile opportunity to highlight their cause.In a statement Thames Valley Police, who are mounting a huge security operation to safeguard the event, said: “We will be working closely with our partners to deliver a safe, secure and happy event for all. He wrote: “Any attempt by the police to disrupt protest in order to serve the interests of the royal household would be wholly inappropriate. Comments from police forces in the past have suggested that there is a real danger this will happen in Windsor. “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 Habgood has yet to reply to Mr Smith, but Thames Valley Police have said it would be for senior commanders on the ground to decide what would constitute a threat to the wedding or an attempt to disrupt proceedings and intervene accordingly.