Universities faced calls to be more "open and transparent" about their admissions policies this week, after a report found that pupils taking "soft" A levels were damaging their chances of getting a place at research-intensive institutions.
The think-tank Policy Exchange accused universities of an "unacceptable" lack of transparency over the A levels they preferred applicants to have, and of failing to properly advise comprehensive school pupils about entry requirements.
Research by the group under the Freedom of Information Act suggests that pupils - largely drawn from comprehensive schools - studying law, media studies, accounting, business studies and psychology are less likely to get places at research universities than those with traditional A levels.
Its report, The Hard Truth about Soft Subjects, says that thousands of pupils studying A-level law, for example, were unlikely to gain places on law degrees at the most selective universities.
While the London School of Economics explicitly lists law as a "non-preferred subject", Policy Exchange said that other universities in the Russell and 1994 groups of research-intensive institutions privately viewed law A level as "non-preferred", but were failing to make this clear to applicants.
Some 96 per cent of the 13,800 pupils that took A-level law last year came from state schools.
University College London's faculty of laws admitted six students with law A level last year, while the University of Durham's Law School admitted 18 students with the A level out of a total of 177 entries.
Durham's website says that it welcomes applicants from students with A-level law, while UCL's says there is "no necessity" for it.
Olga Thomas, who deals with admissions to the UCL faculty, said no bias existed against A-level law and that low numbers of law students with the qualification could reflect a low number of applicants.
A Durham spokesman said it had received 1,513 applications to study law and that all applicants were required to sit the Law National Admissions Test, which was taken into account alongside A-level results, references and achievements in other fields.
Ashley Wilton, head of Newcastle University's Law School, said that while the school accepted applicants with A-level law, the qualification "carries a risk of complacency" as students might underestimate the step up in intellectual standards to degree level.
Tony Downes, deputy vice-chancellor at the University of Reading, said schools taught law A level in a "descriptive way" without reference to the analytical skills needed to study the discipline at university. But Reading changed its stance from discouraging applications from those with the A level to one of neutrality several years ago. "We concluded that there was a risk of discriminating against inadequately advised state-school pupils," he said.
Higher Education Minister David Lammy said: "It is crucial for our institutions to have open and transparent admissions processes to maintain public confidence."
Earlier in 2008, the Government asked the Higher Education Funding Council for England and the Office for Fair Access to give advice on how universities could publish their admissions policies. From spring, institutions will have to produce a Widening Participation Strategic Assessment, setting out their policies.
National Union of Students president Wes Streeting said: "Universities should judge applicants on their potential, not on their awareness of the outdated conventions of the traditional academic elite."