When Birmingham University research fellow Silvia Ramos began teaching three years ago, it took her up to four hours to prepare for an hour's tutorial.
Now she is a course supervisor for a fourth-year project and she is lecturing second-year undergraduates, on top of pursuing her research career in the field of physics.
Dr Ramos is one of an army of postgraduate and postdoctoral students in old universities who shoulder much of the teaching burden. Her experience represents the reality behind the figures released this week by the Higher Education Policy Institute, which show that close to a third (30 per cent) of seminars and tutorials are led by non-academics in pre-92 universities.
Whereas most lectures are still led by academics in both new (99 per cent) and old (98 per cent) universities, some 70 per cent of seminars and tutorials are led by academics in old universities, compared with 92 per cent and 93 per cent respectively in new universities.
Teaching provided by non-academics in old universities often replaces, rather than supplements, the teaching delivered by academics, the Hepi survey found.
The bulk of practical supervision, such as laboratory work, also falls to non-academics in both types of institution. In old universities, non-academics lead 36 per cent of practicals, compared with per cent in new universities.
"If you are spending two or three days a week doing teaching, then it gets in the way if the rest of your workload is really heavy, because you will be evaluated on your research in the end," Dr Ramos said.
"There's an equilibrium to be reached. But when you are in the early stages of your career it is the worst time for having to do everything at once. It is do-able but it does take some serious organisational skills," she added.
Simon Felton, general secretary of the National Postgraduate Committee, said: "Teaching undergraduates is a valuable experience for postgraduates. But it shouldn't be to the detriment of their own studies and research work, and they should be paid properly for it.
"Four hours of teaching work will require four hours of preparatory work."
The NPC is due to update its charter on postgraduate employment with the University and College Union later this month.
Smaller class sizes also tend to feature more widely in new universities, Hepi found. This was a top priority for students, as 31 per cent said they would want to see reduced class and lecture sizes if extra money from top-up fees were available.
Drummond Bone, Universities UK president, said: "The Hepi report illustrates that students want smaller teaching group sizes and better library and academic facilities. Universities are committed to delivering this."
UUK is to lobby for more teaching infrastructure funding in the Government's upcoming spending review.