Students have had their university essays investigated by police and faced questioning by staff under government counter-terror measures, The Independent can reveal.

Campaigners and experts warn that free speech is being stifled on campus and trust destroyed because of the “overzealous” Prevent programme, with students and lecturers becoming “suspects and informants”.

Freedom of Information requests reveal that academic materials have been flagged in response to the government’s anti-radicalisation strategy – but it is understood that no action has been taken against students.

At De Montfort University in Leicester, three students’ essays were flagged to university security before their work was assessed by police.

Meanwhile, at the University of Wolverhampton, a student’s piece of work prompted staff to question the student.

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Waqas Tufail, a senior lecturer in criminology at Leeds Beckett University, called the figures “shocking” and added the new data shows how Prevent has encouraged a “McCarthyite culture” on campus.

He said: “You would not think students’ essays were being policed in a democratic state. In what way can the police be arbiters when it comes to an essay?”

While the flagging of academic texts to Prevent has been previously documented, experts say this is the first time they have heard of universities reporting students for their essays.

The University of Reading faced criticism for flagging an essay by a prominent left-wing academic, which examines the ethics of socialist revolution, as “sensitive” under the Prevent duty.

The new data reveals that some universities also require students and academics to fill out forms before they can access material related to certain topics for their studies.

On the latest data, Dr Tufail, who has carried out research on Prevent, added: “It is just perhaps more evidence that Prevent is not working. And despite what the government has said for a long time, it does discernible harm. It really hits home when you think about the impact on academic freedom and general freedom of speech. There hasn’t been quick enough action from the government.

“I think the government has a lot to answer for. But we shouldn’t let individual universities off the hook.”

The government launched a review of the Prevent programme scheme last January, after years of allegations that it discriminated against Muslims and violated freedom of speech and religion.

But the probe has been beset by controversy, seeing Lord Carlile leave his post as independent reviewer after a legal challenge accused him of bias.

Alison Scott-Baumann, a professor of society and belief at Soas, University of London, found in her research that many academics and students connect “inhibition of free speech” with Prevent.

On the findings showing that students’ work is being investigated, she said: “It completely destroys trust between the staff and the students and it also distorts the subject matter that staff feel they can teach.”

Ms Scott-Baumann, a senior academic whose work involves researching free speech, added: “It suggests to me that because other means of uncovering radicalisation are not working – because there is no radicalisation on campus of a dangerous kind in my view – then if you can’t find what you are looking for you go into essay surveillance having failed to find anything on campus.”

Fope Olaleye, black students’ officer at the National Union of Students (NUS), said: “The level of surveillance being experienced by students, especially vulnerable students, is already having a censorious and chilling effect on who can engage in educational spaces.”

They added: “There is no doubt that the relationship between lecturers and students has changed, from one of partners in learning to that of suspects and informants, and this must change.

“Universities and colleges should be spaces of critical thinking, not sites of surveillance.”

Nick Hillman, director of the Higher Education Policy Institute (HEPI) think tank, said: “While everyone must be live to the dangers posed by extremism, I do worry about the potential chilling effect of Prevent on free speech at universities. The complaints are too loud and come too often to ignore.

“It is ironic that so many academics feel the real threat to free speech comes from the government, when the last Conservative manifesto said free speech needed strengthening in universities.”

Jo Grady, general secretary of the University and College Union, said: “The Prevent programme threatens freedom of speech and stifles debate and open discussion. Staff and students must be free to discuss and debate controversial issues without fear of being referred to the authorities. Prevent does more harm than good if it closes down debate on contentious topics or makes people less likely to speak up.”

A Universities UK spokesperson said: “Universities continue to work hard to implement effective approaches to Prevent that are supported by students and staff, that protect freedom of expression while complying with their wider duties.

“Institutions are committed to promoting and protecting free speech, provided it is done within the law and balanced with safeguarding responsibilities to all students.”