Independent schools say that university departments in key subject areas such as languages and science are relying on them to keep undergraduate courses viable in the face of a "calamitous" drop in applicants from the state sector.
They claim this dependence is being largely ignored as universities increase their efforts to recruit enough students from state schools and poor backgrounds to appease the national access watchdog. Institutions must have their access agreements approved by the Office for Fair Access in order to charge variable top-up fees from 2006.
Writing in Trends in Higher Education Trends this week (page I), Sam Freedman, a policy analyst at the Independent Schools Council, cites modern languages and pure sciences such as chemistry as critical areas.
"In 1995, 15 per cent of new chemistry students came from the independent sector. Now it is 18.5 per cent. In 1995, 26 per cent of new students to study European modern languages came from the independent sector; now it is 30 per cent.
"This is not a question of bias against the maintained sector: a greater percentage of applicants than ever before come from independent schools."
He added: "This trend is even more pronounced at the 'top' universities. At most major universities, modern languages has a proportion of independently educated students greater than the college average.
"Again, this trend cannot be dismissed as 'bias' against the state sector - applications in modern languages are disproportionately coming from the independent sector."
Sir Martin Harris, director of Offa, said that its judgments were based on a knowledge that universities had different recruitment profiles.
"We have been very clear from the start that we are not asking institutions to take more state- school students rather than independent school students."
Roger Woods, chair of the University Council of Modern Languages and professor of German at Nottingham University, said: "I do not see the trend for a higher percentage of language students to come from the independent sector as any kind of indication of bias against the state sector.
"And I see no problem in universities welcoming the importance attached to languages in the independent sector while continuing our efforts to stimulate demand for languages in the state sector."