The UK prime minister has rounded on Belgian authorities for closing down a radical rightwing conference in Brussels that was addressed by British politicians including Nigel Farage and Suella Braverman. After a day of chaos, claims and recriminations, the decision by a local Belgian mayor to stop the National Conservatives (NatCon) event was also condemned as “unacceptable” by Belgium’s prime minister, Alexander De Croo. The two-day conference, which was also due to hear from Hungary’s prime minister, Viktor Orbán, and the far-right French politician Éric Zemmour, had been scrambling to find a venue to host the speakers after two previous venues pulled the plug at the last minute. But within hours of starting proceedings at a third venue, the Claridge hotel, police entered the building to serve an order to close it down. Their action came just as Farage, the former Brexit party leader, was finishing his speech. Emir Kir, the mayor of the Brussels district of Saint-Josse where the Claridge is located, confirmed on Facebook he had issued a ban in order to “ensure public security”. He said the far right – which is predicted to surge in EU-wide elections taking place in June – was “not welcome” in the city. A spokesperson for Rishi Sunak, the UK prime minister, said: “It’s very clear that cancelling events or preventing attendance and non-platforming speakers is damaging to free speech and to democracy as a result. It’s very clear that free debate and exchange of views is vital. Even when you disagree.” De Croo said: “What happened at the Claridge today is unacceptable. Municipal autonomy is a cornerstone of our democracy but can never overrule the Belgian constitution guaranteeing the freedom of speech and peaceful assembly since 1830. Banning political meetings is unconstitutional. Full stop.” The decision to close the conference caused surprise on Tuesday morning as there was little evidence of disturbance at the low-key venue that has previously hosted Brazilian singers and latino festivals. But by 1pm there was bedlam after police tried to serve an order to shut the event down, eventually entering the venue at the invitation of the organisers as Farage was finishing his speech. “I think it’s absolutely monstrous,” Farage told reporters after wrapping up his address. Earlier organisers had blamed “extremists on the left” for trying to suppress free speech and many believed the move to close the event handed a massive publicity coup to NatCon, a little-known organisation. “I’ve experienced cancel culture personally here … but what has happened in there on the stage with global media, we can see that legally held opinions from people who are going to win national elections is not longer acceptable here in Brussels, the home of globalism,” Farage told reporters. “This is the complete old Communist style where if you don’t agree with me, you’ve got to be banned, you’ve got to be shut down.” Organisers allowed Braverman, the former UK home secretary, to go ahead with a lengthy speech before telling the near 100 delegates that they had to leave the building. Braverman, who has sought to cultivate a following on the right in Britain and beyond since she was sacked last year as home secretary, delivered a speech in which she claimed the UK could leave the European convention on human rights (ECHR), scorning Sunak’s recent suggestions that he would be willing to exit from it if it prevented him from implementing his policy of deporting asylum seekers to Rwanda. “It’s therefore no surprise that recent noises in this direction from the prime minister are being dismissed by the public as inauthentic.” After her speech, she told Sky News that the “thought police, instructed by the mayor of Brussels” had sought to undermine free speech and debate. Speakers at the event included elected officials from across the EU, on themes such as “Why Should We Prefer Our Own Culture to Others?” or “Challenging Wokeism: an International Matter”. Among the other speakers in the line-up were Ryszard Legutko, a Polish politician who has said he does not “understand why anyone should want to be proud of being a homosexual” and Rod Dreher, an American writer who argued that the Christchurch mosque gunman who killed 51 people in 2019 did have “legitimate, realistic concerns” about “declining numbers of ethnic Europeans”. Sunak had been urged at the weekend to stop Braverman from attending the rightwing convention featuring figures who have been under investigation for extremism. Organisers insisted they would try to find a new venue for Wednesday when Orbán, who is in Brussels for a leaders summit in the evening, is due to speak. In 2020, the Tory MP Daniel Kawczynski was reprimanded under Boris Johnson’s Conservative party leadership for attending a NatCon event in Rome, where Orbán was also a speaker.