University “safe space” policies are leaving academics afraid to speak their minds for fear of losing their jobs, a professor has claimed.

Dennis Hayes, professor of education at Derby University, suggested there is a “climate of censorious quietude” in universities that means important issues are simply not discussed.

His comments came as universities minister Jo Johnson warned that higher education institutions have a legal duty to ensure freedom of speech.

He said he had written to university bosses out of concern that this duty is being put at risk by policies of “safe spaces and no-platforming”.

The policies – typically put in place by student unions in a bid to protect students from discrimination and language they may find offensive – have led to fraught debate in recent months.

A number of high profile speakers, including feminist writer Germaine Greer and human rights activists Peter Tatchell and Maryam Namazie, have been asked not to appear at events held by some institutions for fear their opinions may be upsetting to some students.

Campaigners say the policies are increasingly impacting on the right to free speech – something they argue is vital within higher education.

During a debate on free speech on campus at a higher education conference held at Buckingham University, Mr Hayes, who is also director of Academics for Academic Freedom (AFAF) said: “There’s so many things that could be discussed, that you dare not say.

“So when you go to university now, you learn what not to say.”

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Mr Hayes suggested there is a belief that someone cannot discuss certain topics, such as abortion, LGBT rights or racism, unless they have direct experience of them, adding that discussing this type of issue “can get you in serious trouble, if not the sack, but you get sent to Coventry”.

“No-one will talk to you.”

“What exists is a climate of censorious quietude in universities. Things are simply not discussed. Academics and students know what they should not discuss.”

Earlier, Mr Johnson told industry leaders at the conference: “Freedom of speech is a core legal duty for universities.

“For a very long time there’s been an obligation on institutions to ensure there is genuinely a climate in which ideas can be challenged and debates can be genuinely entered into.”

He said he had written to Universities UK “out of concern that this duty that universities have was at risk from safe spaces and no-platforming”.

He said he wanted to remind them that one of their purposes is to create an environment in which people can discuss and challenge ideas.

A report earlier this year by Spiked magazine and the Joseph Rowntree Reform Trust suggested campus censorship has been increasing steadily over the past three years, with a growing number of institutions actively clamping down on ideas deemed not in keeping with campus values.

The Free Speech University Rankings (FSUR), drawn from examining the policies and bans of 115 universities and student unions, found almost two-thirds (63.5 per cent) were “severely” restrictive of free speech, with Russell Group institutions found to be significantly more censorious than average.

The NUS official “no-platform” list contains six groups including the British National Party and Al-Muhajiroun, a banned Islamic network in the UK.