More than a fifth of students in subjects deemed "strategic" by the government come from overseas, the Universities UK (UUK) report found.

Only 29% of postgraduate students in these areas are from the UK, with more than half coming from non-EU countries.

The government says attracting foreign students was a matter of satisfaction. But Universities UK says more home grown researchers are needed.

Strategic subjects are defined as those which are vital on the grounds of wealth creation, diplomacy, international relations and cultural grounds.

They include science subjects, mathematics, technology, engineering and languages.

Chairman of UUK's long term strategy group, Professor Geoffrey Crossick, said the lack of UK-born postgraduate students was leading universities to fill their posts with foreign applicants.

The figures underscored "the importance of international students, not only for the financial health of UK higher education, but also for the renewal of disciplines in many areas and in underpinning the UK's world-class research base."

He added: "The concern is that should people return home, the flow of researchers will dry up and that will cause problems for the UK economy.

"The important thing for UK universities now is not to have fewer researchers from abroad but to build up more from the UK."

There are also fears that the lack of home grown researchers could add to the shortage of specialist teachers in these areas in schools.

There are particular concerns about the numbers of students studying physical sciences, within which chemistry has fallen by 19% and physics by 6% over the past 10 years.

The drop-off has led to the closure of a number of university science departments in recent years.

At the same time the number of students studying for degrees in "trendy" subjects like psychology, (up 113%) computer science, law, media studies, drama and film (up 335%) has increased.

Surprisingly, the report added that university graduates with degrees in many of these strategic areas were more likely to be out of work than other graduates.

While the unemployment rate across all graduates in 2005 was 6.6%, for those with degrees in the strategic subjects, it was 8.4%.

This goes against claims that businesses are finding it increasingly difficult to find staff with the appropriate science and engineering qualifications.

A recent survey by the Confederation of British Industry suggested 80% of engineering and industrial companies and 67% of energy, water or utility companies were expecting a shortfall in overall graduate recruits this year.