Suella has been condemned by a group of MEPs over the arrest in London of a French publisher who was interrogated by counter-terrorist police about his political views and “anti-government” contacts.

Twelve MEPs wrote to the home secretary to express their outrage at the “scandalous treatment” of Ernest Moret, who was detained for almost 24 hours and whose iPhone and laptop remain in the hands of the British police.

The European politicians accused the British government of infringing basic human rights and abusing anti-terrorism laws.

The French government is also being urged by French MPs to explain its role in the arrest of Moret in London on Tuesday.

Moret, 28, a rights manager at the radical publisher Éditions la Fabrique, had travelled to London for a book fair. He was quizzed by police about participation in a recent protest in France and asked if he supported Emmanuel Macron, in what his lawyer, Richard Parry, condemned as an “abuse of power”.

In their letter to Braverman, the MEPs – including politicians from France, Germany, Ireland, Portugal and Spain – accused the British government of complicity in the French government’s crackdown on protest.

They wrote: “The police officers claimed that Ernest had participated in demonstrations in France as 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.”

They added: “We consider these actions to be outrageous and unjustifiable infringements of basic principles of freedom of expression and an example of the abuse of anti-terrorism.

“This assault on the freedom of expression of a publisher is yet another manifestation of the slide towards repressive and authoritarian measures taken by the French government in the face of widespread popular discontent.”

Meanwhile, two leftwing French MPs, Aurélie Trouvé and Hadrien Clouet, have written to France’s minister of justice, Éric Dupond-Moretti, asking him to “shed full light” on the French government’s role in Moret’s arrest.

They said they hoped it was not the “result of an agreement between the British and French services to repress participation in demonstration”.

Trouvé accused the French of outsourcing intimidation to the British. She said: “Ernest’s account of his interrogation suggests that the British authorities were really acting on a request, with a script, from the French police authorities, as the questions he was asked concerned exclusively his political and intellectual activities in France.

“The French men and women who demonstrate and mobilise have been under pressure and repression for weeks, but this is a totally unprecedented case, which marks a very serious transgression. We do not intend to leave it at that.”

The French government has yet to respond.

A Home Office spokesperson said: “We thank the MEPs for their correspondence. The letter will be processed and a response provided in due course.”

It is understood there is no evidence to suggest Moret posed any risk to the UK.

Moret, who had more than 30 appointments arranged at the London book fair, returned to Paris on Wednesday, two days earlier than he planned. He was ordered to report back to counter-terrorist police in London next month.

Moret’s employers published a French translation of a book on direct action called How to Blow up a Pipeline, which was recently made into a film. Its Swedish author, Andreas Malm, joined international condemnation of Moret’s arrest.

He said: “Being asked to name ‘anti-government authors’ is obviously scandalous in the extreme.

“This has to be understood in the context of developments in France, which has seen a groundswell of popular protest in recent weeks and months – on both social and environmental issues – and the ever-more ferocious response from the French state.

“With the arrest of Ernest Moret, the French state has clearly outsourced the ongoing crackdown to the British state. Apparently Brexit hasn’t stopped the police services from collaborating across borders.

“The British police here teamed up with the French in a blatant assault on the freedom of expression.”

Matthew Weaver and Dan Sabbagh