The proportion of university teachers aged over 50 is rising at an alarming rate, according to the Association for University Teachers.
An analysis shows that the age profile has increased considerably over the past five years, with the proportion of over-50s up from 22 per cent of academic staff to 28 per cent.
Since most staff can take early retirement from 50, the figures cast a shadow over government plans to increase the participation rate in higher education, according to AUT spokesman Andrew Pakes.
"Without sufficient teaching staff, it will not be possible for universities to deliver the kind of student increases envisaged by the government," he said.
Sandi Golbey, of Nottingham University AUT, said that attracting graduates into a career in academia was harder than ever.
"Most of our brightest students probably look at us and think we must be mad to be working here," she said.
"They can see the amount of overwork and underpay and much more attractive salaries elsewhere."
The AUT analysis found a patchy picture in different areas of academic work.
Research-only staff were much more likely to be under 40 compared with their lecturing counterparts. And lecturers were retiring much earlier with the average age down to 56 in some areas.
The age profile is expected to go on rising until at least 2010, according to the AUT.
* Nominations for the post of general secretary of the Association of University Teachers are to be open, writes Cherry Canovan .
The election will use a "twin track" system, with the national executive selecting an official candidate alongside open nominations of members and staff.
Advertisements for official candidate applicants, who need not be AUT members, will appear in the press next week.
Nominations will close on November 5 and the official candidate will be announced on November 28.
By mid-December, if there are two or more candidates, the membership will be balloted, with the result announced on March 25.