The proportion of academic staff on fixed-term contracts has fallen by 8 percentage points in the past five years, according to official figures.
The biggest change is among research-only staff, according to data released by the 中国A片 Statistics Agency, with the percentage on permanent contracts rising 15 percentage points from 11.1 per cent in 2004-05 to 26.1 per cent in 2008-09.
The proportion of teaching-only staff on permanent contracts also increased by nearly 14 percentage points over the same period, from 38.3 to 52 per cent.
Mike Moore, chair of Universities Human Resources and director of HR services at the University of East London, said the trend was "very good news".
He credited the revised Concordat to Support the Career Development of Researchers, published in 2007, for the rise in the percentage of research-only staff on permanent contracts.
But Sally Hunt, general secretary of the University and College Union, was concerned that open-ended contracts offered no greater job security than fixed-term contracts.
"UCU welcomes the slight reduction in the use of fixed-term contracts. However, nearly three-quarters of research staff and nearly half of all teaching and scholarly staff remain on these contracts," she said.
The Universities and Colleges Employers Association said that the large percentage of staff who remained on fixed-term contracts could be attributed to "full-time research staff with research funding often being fixed, or part-time teaching staff who choose to teach one course or a couple of lectures a week because they prefer the flexibility to combine this work with additional or freelance work elsewhere".
The Hesa data show that for all academic staff, 64.8 per cent are on permanent contracts and 35.2 per cent on fixed-term deals; female staff are slightly less likely to be on permanent contracts (61.4 per cent) than their male counterparts (67.4 per cent).
They also show that younger academic staff are far more likely to be on fixed-term deals: 72.6 per cent of those aged under 30 are, compared with 22.8 per cent of over-40s.