More than 12,000 students with at least one A* grade pass at A-level will be turned away from Oxford and Cambridge this year.
The figures put a question mark over whether the new A* grade – introduced for the first time last year – is doing its job in helping élite universities select the brightest candidates for popular courses.
They will also increase pressure on ministers to allow pupils to apply for university places after they have their A-level results – rather than award them places on predicted grades.
In all, 18,000 hopefuls who applied to the two universities – the vast majority were predicted to get at least one A* grade pass among a clutch of A grades – have failed to obtain an Oxbridge place.
This year, for the first time, Oxford insisted on two A* grades for maths courses and one for science. Cambridge made at least one A* grade the minimum requirement for all its courses last year.
Oxford saw 17,299 applications – 12,063 of them from the UK – for 3,200 places. At Cambridge, there were 15,344 applicants – of which just 3,879 were made offers.
In all, around 18,000 UK applicants are likely to be disappointed with between 12,000 and 13,000 of them expected to have achieved at least one A* grade pass.
Professor Alan Smithers, director of the Centre for Education and Employment at Buckingham University and a senior adviser to the Commons select committee on education, said: "They're awarding places on predictions and then we find out what happens with the results, which is not helpful.
"I think the A* would help to tell the applications apart if the decision was based on actual A-level results. But, as things stand, the A* isn't packing the punch that it might."
He said the present system put more pressure on universities to conduct their own admissions tests to determine which candidates they should take.
Some academics believe a switch to post A-level application would allow universities to look at individual marks as well as grades to help them select those who obtained A* grades with flying colours.
However, Professor Smithers counselled against that, arguing: "I wouldn't want to get into a position where a candidate with 86.5 per cent was automatically considered above one who got 86 per cent. You have to look at potential, too."
In its submission to the Office for Fair Access, the university access watchdog, Cambridge said that last year only 24 per cent of the 13,000 applicants from UK schools and colleges could be accepted.
Of those, 93 per cent had more than the one A* grade necessary to be considered for a place. The average per student was 2.5 A* grades.
Of those accepted at Oxford last year, 88 per cent obtained an A* and two A-grade passes and 38 per cent got three A* grades.
There were 4,626 applicants with at least one A* grade pass who failed to obtain a place.
"Our approach to admissions is necessarily highly selective," the university said. "It is geared towards identifying the best 3,200 candidates from a highly talented applicant pool.
"It is thus inevitable that Oxford will be turning away thousands of candidates who are capable of achieving at least three As."
How the star was born
The A* grade was first awarded last year when 8.1 per cent of A-level scripts (roughly around 60,000) were awarded it.
It was supposed to be an aide to university admissions officers who had long complained they could no longer select the brightest candidates for their most sought-after courses.
This was because of the plethora of A-grade passes awarded – 27 per cent last year up from 26.7 per cent in 2009.
However, some observers said the A* was in danger of soon becoming the new A grade – pointing out that in the 1960s only 8.5 per cent of A-level scripts were awarded the top grade pass, a similar amount to those given A* grades last year.
Universities still award places on students' predicted grades although research shows up to 50 per cent of these may be wrong. If students applied to universities after they received their A levels, that would make the task easier for admissions staff.
However, it would take exam boards and universities out of their comfort zones by having either to move forward the timing of exams or move back the start of the university term.