The government's plans to expand university places will mean that hundreds of thousands of graduates will not find jobs that repay their investment in higher education, according to new research out today.

A book written by Phillip Brown, of Cardiff University, and Anthony Hesketh, of Lancaster University, reveals that 40 per cent of recent graduates are in jobs which do not require degree-level skills three years after finishing their studies.

The book quotes figures showing that starting salaries for graduates are falling, with the average last year of £12,659 substantially lower than the £13,422 in 2002.

The research comes as ministers embark on a last-minute push to win backbench support for a crucial vote on the Higher Education bill on Wednesday.

One government business manager told the Times: "It could be as close as it was in January."

Meanwhile sources close to education secretary Charles Clarke are reported as accusing rebels of colluding with the Tories.

But the Guardian reports he will offer more concessions to critics in a bid to avert a repeat of the previous five vote knife-edge result.