A chemical weapons expert has been disinvited from giving a keynote speech at a UK-run expert conference after civil servants discovered social media posts he wrote criticising Conservative ministers and government migration policy. Dan Kaszeta is one of at least eight speakers banned from government events by an opaque vetting scheme introduced by Jacob Rees-Mogg in 2022, a policy that the banned expert described as an attack on free speech. Kaszeta said: “I’m not a revolutionary communist. I’m a Lib Dem.” He said he had no detailed explanation as to which posts had led to him being disinvited from addressing a specialist event that began on Tuesday. In January, government officials asked Kaszeta, who has more than 25 years’ experience in the field, to address the Chemical Weapons Demilitarisation Conference in London. He said the officials offered to waive a registration fee so he would speak. But in early April, that offer was withdrawn when a civil servant wrote to him to explain that new government rules required that “the social media accounts of potential speakers must be vetted” before they could speak at official events. “The check on your social media has identified materials that criticised government officials and policy,” the email continued, without indicating which postings were deemed unacceptable, or offering Kaszeta a right of appeal. Kaszeta is a frequent user of Twitter. A few days before the ban email was received in April, he shared a thread of tweets comparing Tory MP Nadine Dorries to a series of car crashes and wrote “Bloody Tories” to accompany a news headline that said “Afghan pilot who served with British forces and fled to UK in small boat facing deportation to Rwanda”. Originally from the US, Kaszeta previously worked in Bill Clinton’s and George W Bush’s administrations as a chemical weapons expert, then in the US Secret Service, before relocating to the UK 15 years ago to work as an expert consultant. The 54-year-old gives advice to governments around the world about chemical weapons, including to officials and police in the UK. After the ban, when asked whether his specialist skills were any longer needed in Britain, he said: “Am I banned from other things too?” Cabinet Office officials have the right to go back over five years of social media postings as part of the vetting policy, although its detail has never been publicly released, despite a pledge to deposit it in the Commons library. It was introduced after colonial historian Prof Priyamvada Gopal was banned from speaking to Home Office officials. She had accused the then home secretary, Priti Patel, of bringing “ferociously anti-black attitudes” to government in a tweet highlighted by the rightwing Guido Fawkes website. Colin Talbot, an emeritus professor at Manchester University and expert on the civil service, said he was aware of eight academics who had been banned under the policy. They include AI expert Kate Devlin, banned from giving a talk to a civil service network relating to women in science. Kaszeta said the talk he intended to give was not going to be party political, and would have touched on themes such as “what if Egypt comes clean on having an historic chemical weapons programme? What happens if North Korea implodes? What happens we find a bunch of highly toxic substances turning up in Russia?” It was legitimate for people to tweet out political opinions, Kaszeta said, describing the ban as “a freedom issue” and a category mistake. “It’s like getting thrown off Bake Off for being a Tranmere fan,” he said. “I don’t think there is a millimetre of difference between me and the government on North Korea.” As well as being a specialist consultant, Kaszeta is an author of military history and a member of the Lib Dems and sits on the parochial church council that helps run St Martin-in-the-Fields church on Trafalgar Square. A spokesperson for the Ministry of Defence said: “We carefully consider all our speakers at any government hosted conference to ensure that we can have careful discussion around our policies and procedures.”