A French publisher has been arrested on terror charges in London after being questioned by UK police about participating in anti-government protests in France. Ernest Moret, 28, a foreign rights manager for Éditions la Fabrique, was approached by two plainclothes officers at St Pancras station on Monday evening after arriving by train from Paris to attend the London book fair. He was questioned for six hours and then arrested for alleged obstruction in refusing to disclose the passcodes to his phone and computer. His treatment was condemned as an attack on the right to demonstrate, amid calls for protests outside the UK embassy in Paris and the French Institute in London. Moret arrived at St Pancras at 7.15pm with his colleague Stella Magliani-Belkacem, the editorial director at the Paris-based publishing house, to be confronted by the two officers. Magliani-Belkacem told the Guardian: “When we were on the platform, two people, a woman and a guy, told us they were counter-terrorist police. They showed a paper called section 7 of the Terrorism Act of 2000 and said they had the right to ask him about demonstrations in France.” She added: “I’m still shaking. We are in shock about what happened.” She said French publishers had drafted a joint letter calling for a protest outside the British embassy in France on Tuesday evening about Moret’s treatment. When the officers began questioning Moret, Magliani-Belkacem called her friend Sebastian Budgen, a senior editor at Verso Books in London, at whose home she and Moret had arranged to stay. Budgen arranged for a lawyer to visit Moret. The lawyer called Budgen at 1am on Tuesday to confirm that Moret had been arrested over his refusal to tell police the passcodes to his confiscated phone and laptop. He was transferred to a police station in Islington, north London, where he remained in custody on Tuesday. He was later released on bail. Éditions la Fabrique is known for publishing radical left authors. Moret also represents the French science fiction novelist Alain Damasio and had arranged more than 40 appointments at the London book fair. A joint press release from Verso Books and Éditions la Fabrique condemned Moret’s treatment as “scandalous”. It said: “The police officers claimed that Ernest had participated in demonstrations in France as a justification for this act – a quite remarkably inappropriate statement for a British police officer to make, and which seems to clearly indicate complicity between French and British authorities on this matter.” It added: “We consider these actions to be outrageous and unjustifiable infringements of basic principles of the freedom of expression and an example of the abuse of anti-terrorism laws.” The statement said a protest was planned at the French Institute in London and called on France’s ambassador to the UK, Hélène Duchêne, to request Moret’s immediate release. Budgen said: “It is causing a stink at the London book fair and there’s a big stink in France as well … there’s been an increasingly repressive approach by the French government to the demonstrations, both in terms of police violence, but also in terms of a security clampdown.” Hundreds of thousands of people took to the streets in France last month over Emmanuel Macron’s use of constitutional executive powers to push through an unpopular increase in the pension age. The protests caused King Charles’s planned visit to France, his first overseas tour as monarch, to be postponed. The writers’ association Pen International said it was “deeply concerned” that Moret was detained on counter-terrorism grounds. Pamela Morton, senior books and magazines organiser for the National Union of Journalists, also expressed concern. She said it seemed “extraordinary that the British police have acted this way” in arresting a publisher on the way to the London book fair. “We will be taking this up with the police,” she added. A Metropolitan police spokesperson said: “At around 7.30pm on Monday 17 April, a 28-year-old man was stopped by ports officers as he arrived at St Pancras station, using powers under schedule 7 of the Terrorism Act 2000. “On Tuesday 18 April, the man was subsequently arrested on suspicion of wilfully obstructing a schedule 7 examination, contrary to section 18 of the Terrorism Act 2000.”