There are now so many students seeking A-level and degree status that the Government will find it nearly impossible to create "parity of esteem" for job-related training, said Professor Alison Wolf of London University's Institute of Education.
Her conclusions make gloomy reading for the Government. Attempts to raise the status of vocational education are central to its policy and to much of Sir Ron Dearing's recent review of 16-19 education.
But, according to Professor Wolf, speaking in her inaugural lecture this week, Britain's promotion of work-related training for the young has been "an abject failure". It is, she said, fatally undermined by a "critical mass" of students with academic certificates; both employers and employees have come to seeacademic qualifications as the way to the best jobs.
Schemes to dismantle this educational hierarchy are bound to fail, she said. "In my view this pattern is now irreversible. It is a function of the need for young people to be seen as relatively high-achieving, relatively desirable as employees, relatively high up the distribution in their essentially norm-referenced world.
"It will prove impossible to make vocational education a popular or desirable option for the young. We're trying to do something that simply can't be done."
The pattern in Britain, she said, is repeated abroad. In France, the hardest version of the general baccalaureat, option C (mathematical), is increasingly popular.
Even in Germany, famed for its well-respected vocational training system, more and more students are choosing academicqualifications.
"Vocational education and training have, in this country, enjoyed an almost undisputed reputation as the engine of future economic success. However, when you look at the pattern of demand, not only in the UK but throughout the world, what you find is a flight away from vocational education and towards general academiceducation."
Professor Wolf believes that mass participation in further and higher education means that the best employees are now likely to carry A-levels or degrees.
"What I want to argue is that once you, as a society, reach a certain point, you are effectively destined or doomed to carry on. Once a certain proportion of the population is obtaining particular credentials, the pressure on the remainder to do so increases enormously." Forty years ago, she said, any employer would know that the vast majority of able and desireable employees were to be found among non-graduates.
Now, however, employers are reaching a different conclusion. "Educational qualifications have become a more and more powerful predictor of employment prospects and later success."