The news that David Willetts, the universities and science minister, has expressed his support for a system in which students apply to university with "real" exam grades in their pocket rather than predicted grades will sound familiar to many in the education sector.

Ministers have been trying to introduce a system of post-qualifications applications (PQAs) for years, but none has succeeded.

Many people agree that the move to a PQA system would be more logical than England's existing system, which sets it apart from many other countries (see box, below). Under the current regime, students apply to university before taking their final school-leaving exams, and universities offer places based on teachers' predictions of how their pupils will do. More than half of the predictions are wrong.

However, changing the system presents a series of logistical problems no one has ever managed to solve despite three reviews by Universities UK and a further two by the former Department for Education and Skills.

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The key "sticking point", says Geoff Parks, director of admissions at the University of Cambridge, is the issue of timetabling.

Universities say they cannot wait until exam results are released in August to process applications, as this would mean completing the admissions process in an unfeasibly short time.

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"Fundamentally, you need longer between the end of school exams and, in particular, the release of the results and the start of the university term," explains Parks.

Universities have been reluctant to delay the start of the academic year until January, arguing that they would lose teaching time. A later start could also deter international students, who might choose to study in countries that begin their academic year earlier.

Schools, in turn, have been reluctant to finish their term earlier and lose teaching time, and teachers do not want to see any intrusion into their school holidays.

Time and time again, the education sector has reached stalemate.

Lord Dearing backed the idea of PQA in his National Committee of Inquiry into ³ÉÈËVRÊÓƵ in 1997. Five years later, Sir Mike Tomlinson's inquiry into A-level standards recommended that a PQA system be considered.

In 2004, Steven Schwartz's review of university admissions, Fair Admissions to ³ÉÈËVRÊÓƵ: Recommendations for Good Practice, backed PQA on the grounds that "such a system is likely to be fairer and more efficient". The committee said the current system could not be fair "since it is based on data that are not reliable, it is not transparent for applicants or institutions, and may present barriers to applicants who lack self-confidence".

The issue of PQA was raised once again in December 2010 when Mary Curnock Cook, head of the Universities and Colleges Admissions Service, told a conference that moving to a PQA system was "probably the biggest single reform we can do in the qualifications arena". Although the issue had "gone out of fashion" and had been put in the "too difficult to handle box", she intended to revive it.

"What happened to technology?" she asked the Westminster Education Forum event. "I can't believe that in the next five years we cannot speed up the marking of exams."

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Next came reports that Willetts was in favour. He has indicated that proposed reforms will be floated in the White Paper due in early spring. Meanwhile, Ucas has announced a root-and-branch review of all parts of the university admissions process.

So how might PQA work?

In 2005, after the Schwartz review, the government put two options on the table. Under one, no offers would have been made to students until the exam results were out, although students could submit "expressions of interest" in advance and attend interviews and open days.

The other system would have seen universities reserve a quota of places for students who wanted to change their applications, or apply for the first time, after receiving their results.

Neither option achieved widespread support but, in the end, an "adjustment period" was introduced in 2009. This allows students who have done better than expected to try to "trade up" to a course with higher entry requirements during a five-day period after the exam results are released.

However, because universities have not been required to hold back any places, and owing to the recent pressure on places, only a handful of students have benefited. The number of applicants placed via adjustment in 2009 was 382, and in 2010, 377.

John Morgan, the former president of the Association of School and College Leaders, calls the adjustment period "very complicated" and "a political sop invented by vice-chancellors".

However, Matthew Andrews, chair of the admissions group of the Academic Registrars Council, fears that arguments in favour of PQA are often too simplistic.

"If the question is 'is it better for a student to be considered on their actual grades (rather than) their predicted grades?' then of course the answer is 'yes'," he says. But he is not sure that this is the right question. In his view, the sector should be asking "what is the best system to support widening participation?" - and the answer to that is less clear.

The assumption has often been that poorer students are less likely to apply to top courses because their grades are under-predicted. The 2005 Ucas study Estimating the Reliability of Predicted Grades, by University of Oxford academics, showed that only 45 per cent of predicted grades were accurate.

Most predictions were only one grade higher or lower than the actual exam result. But, in 47 per cent of cases, teachers predicted grades that were better than the pupil achieved. Only 9 per cent of grades were under-predicted.

The same study found that students from lower socio-economic groups were even more likely to have their grades over-predicted.

Unsurprisingly, teachers were most able to accurately predict grades at either end of the scale. Independent schools were the most likely to make accurate predictions.

Andrews fears that PQA could lead to a more "rushed" system in which universities would have less time to build up a relationship with their students.

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"Research has shown that students who make late decisions in clearing are statistically more likely to drop out during their course," he points out.

Others worry that a move to actual grades might make the admissions process more mechanistic, putting a greater emphasis on exam grades and reversing recent efforts to examine candidates "in the round".

According to Andrews, there may be more effective ways to widen participation that would require less upheaval.

"Sometimes this issue can be made light of - people say, 'oh the problem is you just can't get the exam results out a couple of weeks earlier' or 'universities aren't willing to move their term back a few weeks' - but it is not a trivial undertaking," he says.

Nevertheless, the Sutton Trust, a charity dedicated to fair access, is strongly in favour of PQA. Its chairman, Sir Peter Lampl, believes that it would particularly empower bright students from poor backgrounds who "often lack the support and guidance needed to navigate a higher education world".

The Million+ group of new universities supported PQA last time it was proposed. However, Les Ebdon, chair of the group, suspects there will be little appetite for it in the current climate. "I think that people will say, 'We're going through so much change that we need this like we need a hole in the head.'"

Advocates argue that the current climate with its funding constraints makes PQA all the more attractive. It would be much more efficient and would vastly reduce the administrative burden placed on universities. At present, students make up to five applications for a university place simultaneously, meaning that institutions process thousands of applications that are never taken up.

It might also make the difficult juggling act played by admissions tutors more manageable.

Helen Johnson, deputy director of admissions (undergraduate) at the University of Birmingham, explains the complexity. During the confirmation and clearing periods of the admissions process, her team, which handles about 40,000 applications a year, must wait to see how many students who have selected Birmingham as their "insurance" choice (their fallback option if they do not get the grades their first-choice university requires) take up the offer before they can decide whether to accept "near misses" - students who have fallen just short of what their Birmingham offer requires.

"Of course the 'insurance' people we're waiting for are someone else's 'near misses'," says Johnson. "It is a sort of 'who blinks first' game."

And the introduction of financial penalties for universities that over-recruit means that "the stakes get higher every year".

For Parks, these arguments in favour of PQA are "pretty much unanswerable". He says that Cambridge has long been supportive, and PQA would probably result in the university having to interview far fewer applicants.

The autumn term at Oxbridge starts later than at other universities, but he thinks there would be "a very strong argument" for Cambridge starting in mid-October rather than at the start of the month if that would help to bring about PQA.

At sixth-form level, he says, there is "quite a lot to be said" for the idea of pupils finishing their exams earlier, leaving them time to research university choices during the summer term rather than having to juggle the research alongside their AS levels.

Morgan is optimistic, claiming to have "seen a change in attitude" among Russell Group admissions tutors.

Meanwhile, technology has moved on, allowing many processes to be speeded up. Ucas now handles applications online. Many universities are centralising their admissions processes and shifting to electronic systems.

A spokesman for Edexcel, one of the major exam boards, said he was "confident" that the board could process and mark exam scripts and award grades to students as quickly and accurately as possible "in a shorter timeframe if needed".

Finally introducing PQA, says Parks, will certainly require strong political will.

"If everyone is willing to give a bit, I can't see why it is impossible," he says. "But then I'm an engineer and we see problems as solvable."