UCL Union was scheduled to open the no-confidence motion - critical of Professor Grant's decision to accept a government appointment to lead the reshaped NHS - to a referendum of all students on 19 January. The vote is scheduled to close on 26 January.

Last month, Rex Knight, UCL's vice-provost (operations), wrote in a letter to the union's trustees that the no-confidence motion - already passed by the union's executive and a members' meeting - has been "undertaken without any consideration of the potential huge reputational impact for both UCL and UCLU".

Mr Knight said the vote "is bound to have a significant impact on the relationship (between the union and the university), our approach to future investment and our view of the roles and responsibilities of the union".

Michael Chessum, a UCL undergraduate and former students' union officer, said: "I imagine that Malcolm Grant would be under very real pressure to go if the motion passes."

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Mr Chessum said that pressure would come not from the senior management team - which has expressed full confidence in Professor Grant - but "within UCL more broadly and among academics".

He said UCL was concerned that, after a period of being "quite a low-profile campus politically" it was "faced with an explosion of campus radicalism and people who are willing to occupy various spaces on campus".

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A UCL spokesman said the "vast majority" of students were very happy with their experience at the college, according to the National Student Survey, and only a "tiny minority are engaged in this debate".

He added: "We note their concerns, but student politics have always enabled small numbers of individuals to pursue their interests, without having any impact on the life of the university."

john.morgan@tsleducation.com.