A masters student researching terrorist tactics who was arrested and detained for six days after his university informed police about al-Qaida-related material he downloaded has spoken of the "psychological torture" he endured in custody.

Despite his Nottingham University supervisors insisting the materials were directly relevant to his research, Rizwaan Sabir, 22, was held for nearly a week under the Terrorism Act, accused of downloading the materials for illegal use. The student had obtained a copy of the al-Qaida training manual from a US government website for his research into terrorist tactics.

The case highlights what lecturers are claiming is a direct assault on academic freedom led by the government which, in its attempt to establish a "prevent agenda" against terrorist activity, is putting pressure on academics to become police informers.

Sabir was arrested on May 14 after the document was found by a university staff member on an administrator's computer. The administrator, Hisham Yezza, an acquaintance of Sabir, had been asked by the student to print the 1,500-page document because Sabir could not afford the printing fees. The pair were arrested under the Terrorism Act, Sabir's family home was searched and their computer and mobile phones seized. They were released uncharged six days later but Yezza, who is Algerian, was immediately rearrested on unrelated immigration charges and now faces deportation.

Dr Alf Nilsen, a research fellow at the university's school of politics and international relations, said that Yezza is being held at Colnbrook immigration removal centre, due to be deported on Tuesday.

"If he is taken to Algeria, he may be subjected to severe human rights violations after his involvement in this case. He has been in the UK for 13 years. His work is here, his friends are here, his life is here."

Of his detention, Sabir said: "I was absolutely broken. I didn't sleep. I'd close my eyes then hear the keys clanking and I would be up again. As I realised the severity I thought I'd end up in Belmarsh with the nutcases. It was psychological torture.

"On Tuesday they read me a statement confirming it was an illegal document which shouldn't be used for research purposes. To this day no one has ever clarified that point. They released me. I was shaking violently, I fell against the wall, then on the floor and I just cried."

Bettina Rentz, a lecturer in international security and Sabir's personal tutor, said: "He's a serious student, who works very hard and wants a career in academia. This is a great concern for our academic freedom but also for the climate on campus."

Students have begun a petition calling on the university to acknowledge the "disproportionate nature of [its] response to the possession of legitimate research materials".

A spokesman for Nottingham University said it had a duty to inform police of "material of this nature". The spokesman said it was "not legitimate research material", but later amended that view, saying: "If you're an academic or a registered student then you have very good cause to access whatever material your scholarship requires. But there is an expectation that you will act sensibly within current UK law and wouldn't send it on to any Tom, Dick or Harry."

At its annual conference next week the University and College Union will debate a motion on "assaults on academic freedom by the DIUS [Department for Innovation, Universities and Skills]". Sally Hunt, general secretary of the UCU, said: "If we really want to tackle problems like extremism and terrorism, then we need to be safe to explore the issues and get a better understanding. The last thing we need is people too frightened to discuss an issue or research a subject because they fear being arrested or reported."

The higher education minister, Bill Rammell, said: "The government does not want to or has never asked for staff or students to spy on their colleagues or friends. We want universities to work with staff and students on campus to isolate and challenge the very small minority who promote violent extremism."

Sabir's solicitor, Tayab Ali, said: "This could have been dealt with sensibly if the university had discussed the issue with Rizwaan and his tutors. This is the worrying aspect of the extension of detention [under the Terrorism Act]. They can use hugely powerful arrest powers before investigating."