All students who undertake any paid employment during term time are putting their degree outcome at risk, according to the most comprehensive study ever undertaken of students' attitudes to debt.
The study, from the Centre for Higher Education Research and Information, found a correlation between students' term-time employment and poorer end-of-year results and degree classifications.
It found that the more hours a student spent working, the worse their academic performance was likely to be - but, crucially, the study says, there is no working hours "threshold" below which there are no negative effects, as suggested in other studies.
"Just by engaging in paid work students are putting their results at risk," it says.
The report, commissioned by Universities UK and the Higher Education Funding Council for England, was submitted in December 2003 but, as The Times Higher reported last week, UUK ordered sweeping cuts of politically contentious elements and prevented its publication before the May 2004 election to avoid criticism of the Government's university funding policies.
The study, which is based on a poll of 1,500 students in higher education in 2001-02, concludes that irrespective of improvements to the overall financial support package available to students from next year, the problem of term-time working will remain.
From 2006, students will be able to claim maintenance grants as well as student loans, and top-up fee payments will be deferred.
"Some students may use the extra available income to reduce or eliminate term-time working, while others may still work in order to minimise their debts," the report concludes. "Overall, it seems most likely that term-time work will remain part of the higher education landscape."
It says that just over half the students worked during term-time in 2000-01 and 2001-02. They worked an average of 14.2 hours a week in 2000-01 and 12.7 hours in 2001-02, their final year of study.
Some 43 per cent worked more than 15 hours a week in 2000-01. At three of the seven universities studied, two thirds of students worked more than 15 hours a week.
For a student who works more than 16 hours a week in term time, the odds of getting a good degree are about 60 per cent those of one who does not work, the report says.
The report says that as poor students and those from minority ethnic groups tend to work more, the issue perpetuated existing disadvantages. It warns that universities taking on greater numbers of non-traditional students could suffer unfair damage to their academic reputations as a result of the negative effects of working.
Claire Callender, one of the report's authors, said: "Term-time employment is an issue the whole sector is going to have to deal with."
A spokesman for UUK said the link between working and performance was a "concern" and the impact of new financial arrangements next year would have to be monitored. "Universities' concern on this issue is also reflected in their provision from next year of some £300 million in new money for bursaries to help the poorest students," he said.