The report noted a 'subtle change' in student attitudes

Of 101 teachers interviewed, 54% said students were often discouraged by the universities' "social context", while 45% said this happened occasionally.

Grammar school and college students were less wary, the National Foundation for Educational Research found.

It recommended more "proactive targeting" of comprehensives.

'Based on merit'

A total of 236 teachers completed the NFER's questionnaires: 101 from comprehensives, 80 from grammars and 55 from post-16 colleges.

Worries about the "social context" of Oxbridge often discouraged pupils, according to 23% of grammar school staff, and occasionally according to 70%.

For college teachers the figures were 46% and 48%.

Some 906 students at comprehensives, grammar schools and colleges were also interviewed.

NFER found 35% were put off applying to Oxbridge by its social mix, down from 47% in a corresponding study in 1998.

'Good progress'

Geoff Parks, director of admissions for Cambridge colleges, said: "Admission to Oxford and Cambridge is based solely on academic ability and potential, and both universities want to ensure that the brightest UK students are applying for, and getting, our places.

"We have worked very hard over the last few years to get that message across to teachers and students so we're pleased that this report shows we are making good progress."

According to the survey, the main perceived differences between Oxbridge and other universities were "prestige" - cited by 26% - and academic reputation, mentioned by 24%.

Some 77% said career ambitions would make students more likely to apply.

Meanwhile, 64% said teaching methods, frequently involving one-to-one discussions with academics, were important.

The report noted a "subtle change" in the way students looked at Oxford and Cambridge since 1998.

In the latest study, 37% described Oxbridge undergraduates as "motivated", up from 23%.

Some 32% thought it cost more to study at Oxford or Cambridge, down from 43% in 1998.

An Oxford University spokeswoman said it was "demonstrably incorrect" to think Oxbridge was more expensive than elsewhere.

Both universities have launched bursary schemes for students from poorer families.

From 2006, Oxford is offering those from low-income homes up to �13,000 over the course of their degree.

Cambridge will provide up to �3,000 a year.