The public spending watchdog is being urged to investigate possible abuse of public funds after some former vice-chancellors doubled their incomes last year.
Sir John Daniel, former vice-chancellor of the Open University, became the highest-paid university head, taking home ?309,000 pro rata. He now has a tax-free salary as director-general for education at Unesco, the United Nations' education and cultural organisation, in Paris.
Mathematician Sir John Kingman, former vice-chancellor of the University of Bristol, doubled his income to ?252,000. He is now chairman of the Statistics Commission and director of the Isaac Newton Institute for Mathematical Sciences at the University of Cambridge.
Frank Gould left the University of East London with 60 per cent more money than he earned the previous year.
Staff unions want to know how such pay rises can be justified. In the next few days, they will ask the Public Accounts Committee to investigate. The unions also plan to press the Council of Chairs of Governing Bodies to ask remuneration committees to publish their methodology and evidence.
Tom Wilson, head of universities at lecturers' union Natfhe, said: "The first port of call is the Public Accounts Committee. It's their job to act as the public spending watchdog as to how public money is spent."
Sally Hunt, assistant general secretary of the Association of University Teachers said: "We greatly criticise the vice-chancellors' back-street deals that go on with remuneration committees and university governance."
According to the Committee on Standards in Public Life, universities should "follow best practice in limiting the use made of commercial confidentiality and in explaining themselves to their communities".
Sir Bryan Nicholson, chairman of the Cookson Group of material technology companies, chairs the remuneration committee and the council of the Open University and is pro chancellor.
He was unavailable for interview but a statement issued on his behalf said:
"Sir John Daniel's contract, when he joined the Open University in 1990, allowed for payment in lieu of study leave. Sir John's workload over the 11 years that he was vice-chancellor did not allow him to take the amount of study leave to which he was entitled. Therefore, under the terms of his contract, he received payment in lieu. This payment was entirely separate from his normal salary."
"The OU regularly considers its employment policies and procedures... payment in lieu of study leave is no longer in the vice-chancellor's contract."
Brenda Jarvis, president of the Open University Association of University Teachers, said: "The OUAUT is very aware that the funding for the Open University comes from two main sources: government funding and Open University student fees. We are therefore concerned that these monies - taxpayers' and students' fees - are spent wisely.
"For a number of years the OU has declined to 'cash in' study leave that is owed but unspent when academic staff leave the OU. In addition, staff have been exhorted to take their study leave in the year it's due."
She said it was surprising that Sir John "was allowed to cash in nearly a year's study leave".
The chairman of the council of the University of Bristol is J. M. Woolley, a Bristol businessman. The university said that Mr Woolley was out of the country and could not be contacted.
A spokesman said: "Sir John Kingman left Bristol last year and took up a post at Cambridge. He had been Bristol's vice-chancellor for 16 years, a period during which the university went from strength to strength. The employment and contractual arrangements that applied to him are a private matter."
The chairman of the governors at the University of East London is Stephen O'Brien, chief executive of London First. Mr O'Brien was in Israel this week and could not be contacted.
A university spokesman said: "In August last year, the then vice-chancellor retired at the age of 64 after holding that office for ten years. Almost all the difference between the published figure of ?189,000 and the previous figure relates to early retirement costs."
Martin Hoyles, secretary of the coordinating committee for lecturers' union Natfhe at UEL, said: "There was uproar here from staff and students about Frank Gould's pay package... but he has gone now and we are looking forward to a more enlightened management."
Statistics: Analysis: What they get could staff a university