Universities are saving about Pounds 50 million a year by illegally exploiting an army of hourly paid lecturers, trade union Natfhe says.
A Natfhe survey extrapolates that more than 15,000 part-time staff across the sector are working at least two or three hours for free for every hour they are paid.
The union said that part-timers are providing the backbone of higher education and are entitled to be put on proper pro-rata contracts, increasing the sector's wage bill by about Pounds 50 million, more than Pounds 3,000 each.
Tom Wilson, head of universities at Natfhe, said: "Of the 30,000 hourly paid teaching staff, well over half ought to be earning 50 per cent more on contracts equivalent to their full-time colleagues."
Natfhe conducted its survey at London Guildhall University, and its figures are roughly extrapolated for the sector as a whole.
The survey found that nearly nine out of ten hourly paid lecturers routinely undertook duties for which they were not paid. Some 86 per cent undertook tutorial work, 76 per cent curriculum planning, and 37 per cent performed student counselling roles. Almost half (44 per cent) were even involved in research.
Natfhe conducted the survey as part of a dispute with Guildhall over staff contracts. The university will not introduce fractional contracts, arguing that hourly paid lecturers do not do the same duties as their full-time colleagues.