Around a fifth (19%) of those working full or part-time were not in graduate professions, according to a study published by the Higher Education Statistics Agency (Hesa).

And more than one in 10 (11.7%) of those who left university in 2004/05 said they had been out of work at least once.

The figures, based on a snapshot of 41,395 university leavers taken on November 28 last year, found that 23.9% of graduates were not in full time paid work.

A further 2.6% were unemployed, this was down from 5.6% of students six months after graduating.

In total, 88.9% of 2004/05 graduates were in some kind of employment three and a half years after leaving university.

But the figures represent students who graduated before the recession hit - and the picture is much gloomier for today's university leavers.

Hesa statistics published in July showed that showed that 16,835 students leaving full-time first degree courses last year, just before the recession tightened its grip, were not in employment six months after graduation.

The figures are expected to soar this year as the recession forces employers to stop recruiting - reducing the job prospects of thousands of graduates.

A survey of the top 100 graduate employers published in July found that vacancies for students leaving university this summer have been cut by 28%.

On average, employers are receiving 45 applications per graduate vacancy, a third more than in 2008, the research said.

Today's figures also reveal men are earning on average £2,000 more than women three and a half years after graduating.

The study found that this was partly because a larger proportion of men were in higher paid jobs.

Sally Hunt, general secretary of the University and College Union said: "We have always argued that university has the power to improve people's quality of life.

"However, the government must not use these figures to justify piling more debt on prospective students or their families. There is a clear economic case to be made for investing in our graduates.

"Aside from the obvious benefits of more teachers, nurses, doctors, engineers etc, graduates are less likely to commit crimes, they are less likely to be a burden on the NHS and less likely to stretch the creaking benefits system."

Pam Tatlow, chief executive of university think tank Million+, said: "Assessing what graduates are doing and what they are earning three and half years after graduation rather than six months after is a much better measure of the benefits of studying for a degree."

She added: "The survey does reveal that a gender pay gap kicks in in spite of graduate qualifications with a larger proportion of men in higher salary jobs and women working part-time earning £3,000 per year less than part-time men.

"Black graduates also have higher unemployment rates three and half years after graduation and this certainly requires further research."

A spokeswoman for the Department for Business, Innovation and Skills said: "This latest survey of the long term prospects for graduates clearly shows that their degree is a good investment for life with unemployment rates remaining low and the vast majority (81.1%) of those working, in graduate level jobs three and a half years after graduation.

"During these difficult times graduates continue to do better than those with lower qualifications, with their average salaries rising about 36% compared to six months after graduation and overall career satisfaction remains high."