Some science and engineering departments will be put at risk by the new funding regime, critics have warned, as newly released data indicate that many classroom-based subjects have greater proportions of the much-prized AAB students.
The Higher Education Funding Council for England has published a breakdown by subject area of students achieving at least AAB at A level or the equivalent.
The data come ahead of the launch of the new system in 2012, when these students will be removed from universities' core quotas, with individual institutions freed to compete to recruit as many AAB students as they wish.
The figures, for home and European Union students for 2009-10, also show the social profile of AAB students: 25 per cent are from independent schools, whereas just 15 per cent of students from the more disadvantaged half of society are AAB (where grades are known).
A number of key science and engineering subjects - which are more expensive to teach - have relatively low proportions of AAB students, including biology (24 per cent of the 4,664 students with known grades), civil engineering (28 per cent of 2,150 students) and mechanical engineering (29 per cent of 2,952 students).
Of the 2,991 students studying chemistry whose grades are known, 35 per cent had AAB.
Some popular classroom-based subjects score higher, including classical studies (60 per cent from 925 students), French (55 per cent from 1,801 students), economics (49 per cent from 5,580 students) and history (41 per cent from 8,890 students).
Among the science subjects to score highly on AAB proportions is physics (59 per cent from 2,530 students). But a report on the recent White Paper by the Higher Education Policy Institute says the long-term impact of the AAB policy "could be damaging to some of our leading science departments" and recruitment patterns should be "monitored closely".
It says that if AAB elite institutions expand in science, other universities could find "a shortage of well-qualified applicants".
"A small and reducing core with which to recruit students with potential, but without high grades, could make it difficult for them to maintain their recruitment of suitably qualified students," the report adds.
James Naismith, professor of chemical biology and director of the Biomedical Sciences Research Complex at the University of St Andrews, said such a scenario would mean "the number of AAB+ students left for the lower-ranked universities within the Russell Group and 1994 Group will decrease".
He added: "Looking at the percentage of AAB+ students suggests these are higher in many non-STEM (science, technology, engineering and mathematics) subjects. Since having AAB+ will be seen as a passport to choice it would be naive to assume we will not see a change in subject choice in schools, to science's and engineering's detriment."
Les Ebdon, chair of the Million+ group of newer universities, said: "It will be easier to recruit AAB students in non-STEM subjects than in STEM subjects."
Under the government's new system, each university will lose 8 per cent of its non-AAB places, forming a pool of 20,000 additional places open to bids from institutions charging average fees of less than £7,500.
However, critics have pointed out that high-cost lab-based subjects could not necessarily be delivered at this lower rate.
Asked whether he believed science departments could close, Professor Naismith said: "If nothing changes in the medium term, yes, I am absolutely sure this would be the outcome. Lab-based traditional physical, biological and engineering subjects will be found in a diminishing number of universities."
Under the new funding regime, high-cost subjects will receive only a reduced allocation of the teaching grant for each student - which has been axed entirely for most subjects.
Imran Khan, director of the Campaign for Science and Engineering in the UK (CaSE), said even the "most expensive institutions" may find that science and engineering subjects bring in negligible income or make a loss, while arts and humanities subjects bring in "a lot of cash up front".
On AAB, CaSE argues that, overall, a greater proportion of STEM students have AAB grades than those who apply for humanities. But the volume of humanities students is greater (177,135 compared with 112,100).
A spokesman for the Department for Business, Innovation and Skills said the proposals "will give more students, of whatever social background, a better chance of going to the university of their choice", and noted that biology and chemistry were in the top 10 most popular subjects for A-level entries in 2009-10.
The Labour Party this week published figures showing the institutions likely to lose the most places to create the 20,000 biddable "margin".
The list is led by Manchester Metropolitan University, which it is claimed could lose between 500 and 550 places.
Restrictions on AAB equivalent qualifications 'may not be legal'
The legality of the government's AAB plans has been called into question, with warnings that it could face costly court action unless it lifts restrictions on the eligible qualifications.
Under plans unveiled in the White Paper in June, universities will be allowed to recruit unlimited numbers of students with grades of AAB or better at A level or the equivalent.
However, the list of "equivalent" qualifications is far more restrictive than that used by the Universities and Colleges Admissions Service, raising concerns that the policy could be challenged by high-achieving students with other credentials.
Students applying from other European Union countries would be particularly disadvantaged, as the proposed list does not include common European qualifications such as the French Baccalaureat and the German Abitur.
According to EU rules, entry criteria should not discriminate on grounds of nationality.
The proposed list, which will come into force in 2012, is limited to awards such as Scottish Highers and Irish Leaving Certificates, vocational courses such as BTEC Nationals, and the International Baccalaureate.
Lawyers told Times Higher Education that the list was open to legal challenge, and raised questions about the failure to include a number of vocational qualifications that attract a score under the Ucas tariff points scheme.
In its consultation on the plans, the Higher Education Funding Council for England says the limited list is needed to define a "predictable" and "stable" number of AAB students.
However, some legal experts have questioned the assumption that opening up the list would create the level of uncertainty that the consultation paper suggests.
In its own modelling of AAB students from the 2009-10 academic year, Hefce found that 56,000 were above the grade threshold, including around 5,000 EU students. It is understood that the majority of the latter held the International Baccalaureate.
A further 17,000 EU undergraduates did not exceed the benchmark, either because they failed to meet the grade threshold, held a qualification not on the list of A-level equivalents, or their entry awards were "unknown".
Chris Snowden, vice-chancellor of the University of Surrey and the new vice-president of Universities UK, said there was a danger that students with high grades in qualifications not included in the Hefce AAB equivalence list could be rejected by institutions.
He said this would not be a "major issue" in the first year or two as there would still be enough places for strong candidates with alternative awards.
But he predicted it would become "more acute" as the government increases the proportion of places removed from universities' general quotas and offered to those charging below £7,500.
Legal challenges over equal treatment of EU students are not without precedent.
The Austrian government was involved in a long-running battle with the European Commission after imposing restrictions on EU students from outside Austria, and the Scottish government is also facing a challenge over its fee regime.
Julian Lonbay, an expert in European law at the University of Birmingham, said access regulated by merit was allowed but "all EU nationals should be in the race for a place".
A European Commission spokeswoman said that if candidates from countries such as France or Germany were turned down "systematically", simply because they did not have a UK grade, then there could be a case for "indirect discrimination".
A spokesman for Hefce said the AAB proposals were "subject to consultation and we could make changes, including adding other qualifications".