Special Branch is investigating activities of extremist Muslim student groups in colleges after reports of intimidation and assaults on campus.
Detectives are keeping a close watch on a number of Midlands and West Yorkshire colleges amid fears of a revival of activity by fundamentalist Islamic sects.
Leaflets distributed this week at Derby College, Wilmorton, by one extremist group called on students to join a meeting in support of Khilafah, a putative pan-Islamic state.
In Bradford Ilkley Community College, nine students have been expelled recently over violent incidents stemming from confrontations over Islamic beliefs.
Special Branch was brought in last month at Derby College after student protests at governors' decision to refuse a request for a permanent prayer room. There were also reports of female students being taunted over allegedly failing to adhere to strict Islamic dress codes.
Those involved in the activities are understood to include supporters of the extremist group Hizb ut Tahrir (HUT, the party of God) - the group behind the leaflet circulated this week. The organisation, banned on several British university campuses after a series of violent demonstrations last year, has distributed literature in the UK demanding the death sentence for homosexuals and calling for a war between Muslims and Jews.
Derby College principal David Croll said governors had followed Association for Colleges guidelines in calling in the police. He said: "One of our biggest concerns was Muslim community leaders' strong disapproval of HUT. We have acted in the interests of Muslim parents and of female students." Special Branch has declined to comment on the investigations.
Police are also being kept informed of activities of Islamic groups, including HUT, at some West Yorkshire colleges.
Dr Paul Gallagher, principal of Bradford College, said HUT had been linked with incidents of verbal and physical abuse against security staff and non-militant Muslim students. "We see these kind of groups as Islamic versions of the National Front. Our college policies do not tolerate extremism in any form," he said.
Other colleges with a high proportion of Muslim students have found no firm evidence of HUT activity, but report growing concern over increased tensions on campus. A manager at one Lancashire college said:"There is definitely evidence that young Muslims are becoming increasingly fervent, which makes us worried. "