Visit the Government’s Diploma website today and you can read that by 2011 pupils will able to take a Diploma in 17 different subjects. It is presented as a bald statement of fact. But it will require a Conservative collapse in the polls for it to turn out to be true. The party has already said that if it wins the next general election it will cancel the final phase of Diplomas due to be introduced in 2011.

This is no surprise. The qualifications in humanities, science and languages are seen as potential rivals to GCSEs and A-levels, a development the Tories have always been opposed to. What has not been known, however, is how a Conservative government would treat the 10 Diploma subjects that have already started and the four slated for introduction this time next year.

Now The TES has learnt that Tory insiders believe the qualifications are so flawed that the current situation is untenable. Instead, the Diploma could be abolished, reformed or simply cut loose from Government and left for the exam boards to develop as they choose, if they think there is a market for it. And that is a big if.

Ashfield School in Kirkby-in-Ashfield, Nottinghamshire, is a pioneer in vocational education that has opened its own business park. Firms such as construction giant Carillion and the RAC occupy state-of-the-art premises rent free at the comprehensive, in return for the training they offer its pupils. It is just the kind of school that should be welcoming the millions the Government has invested in the Diploma, designed to combine practical and academic learning.

Instead, Martin Davies, deputy head, has “massive reservations” about it and will only be offering two subjects to a limited number of pupils. He argues that they take so much space in the timetable that they severely limit other options. Academic pupils who may otherwise have taken a string of GCSEs including humanities and a couple of languages would have that breadth of the curriculum denied.

Mr Davies fears the content of the Diplomas will also put off the less academic. “It is nothing like as practical as you would imagine,” he said. “There is lot of stuff in there that is very theoretical.

“To be successful in a Diploma you would need students with reasonably high academic ability. The students that you might expect to go for work-related learning won’t be getting what they were expecting.”

Mr Davies saw his fears confirmed at a school, deemed to be a centre of excellence for Diplomas, where pupils taking one in construction had to be offered a separate course in brick-laying to keep them interested. After that there was no space in their timetable for anything beyond the core subjects of English, maths, science and PSHE. “That mortified me,” Mr Davies said. “That is tantamount to child abuse.”

His verdict is the latest in steady stream of bad news for the Diploma. In April, heads of two of the big exam boards involved in delivering the qualification warned they were not developing as ministers had hoped.

Simon Lebus, Cambridge Assessment group chief executive, told the Commons’ Children, Schools and Families Select Committee that its introduction was “over-hurried”, “shaky” and added to an already “high risk”. Damagingly for Ed Balls, Schools Secretary, Mr Lebus also described Mr Balls’ aim of the Diploma becoming the “qualification of choice” by 2013 as a “fantasy”.

Jerry Jarvis, Edexcel managing director, told the MPs: “Money is being put on the Diploma, so it has to work. But we just feel that it is too fast.”

Last month, ministers presented Government-commissioned research into universities’ views of the Diploma as demonstrating strong support for it. But the Exeter University study also revealed that there was “concern” among universities with the highest entry standards about the “likely academic rigour” of Diploma content. Moreover, none of the admissions officers spoken to in these “research-intensive” universities “reported high levels of internal support” for the qualification. Phrases used included “quite cynical” and “cautious”.

A week later the first Diploma results were published. They only involved the small number of candidates who squeezed courses designed to last two years into 12 months and exam boards warned of reading too much into them. However, the low pass and completion rates provided the Diploma’s critics with the opportunity to give it another public kicking.

The problem for the Government is that, whatever the truth of the charges being levelled against its reform, when you are launching a new qualification perception is everything. If employers and universities don’t believe the Diploma is credible then pupils won’t opt for it, further undermining its credibility and preventing it from gaining the general recognition necessary for it to have any chance of rivaling A-levels.

The perception problem among young people was illustrated by Reading University research on the Diploma published last week. The study found that more than a third of teenagers had little or no knowledge of the qualification at the start of Year 11. And by the end of the year a quarter still knew nothing about it, compared with A-levels, which 94 per cent of pupils knew something about.

Even more worrying for the Diploma’s backers were the incorrect perceptions pupils had about it. Many thought it only involved studying one subject, that it was a job-specific qualification and that it was a less-academic, second-best alternative to A-levels. Most damagingly, less than a quarter of the pupils surveyed said they would consider taking it.

Any confusion among teenagers about the Diploma seems reasonable as its exact purpose and nature often seems muddled to education experts. To understand why you have to go back to the Diploma’s origins in February 2005, when the qualification was announced as part of ministers’ response to the review of 14-19 education by former chief inspector of schools, Sir Mike Tomlinson.

The Government-commissioned inquiry, which cost #163;1 million and took 18 months to complete, recommended a new overarching diploma. It would end the academic vocational divide by incorporating A-levels and GCSEs alongside work-related courses, eventually subsuming them.

The proposals received almost unanimous backing from the education world, but ministers were concerned about the electoral consequences of abandoning A-levels and GCSEs in the run-up to the 2005 general election. The result was a politically led compromise and the introduction of 14 new work-related Diplomas alongside the traditional academic qualifications, which would remain free standing. Critics complained the solution simply perpetuated the two-tier system that had always seen the vocational side come off second best.

In a bold move in 2007, Mr Balls appeared to try to address their concerns when he announced the introduction of the Diploma in three new academic subjects, to be followed by a review of A-levels in 2013.

He said he thought the Diploma could emerge as “the jewel in the crown of our education system”. It was an intervention that theoretically re-opened the possibility of Mr Tomlinson’s original intention of a diploma bridging academic and vocational education, and replacing A-levels.

But the Tomlinson report would have seen A-levels and GCSEs automatically swallowed up by the diploma. A Tomlinson-style qualification may have been complicated but schools would have opted for it because there would have been nothing else on offer. Instead, Mr Balls has allowed A-levels to remain as independent, potent rivals that the Diploma will have to fight enormous odds to overcome.

And the inherent difficulties in its design that are already starting to emerge will not help. Last month’s Diploma results may only have involved 212 pupils but they were enough to highlight a real problem: functional skills. To pass the qualification pupils have to complete compulsory basic skills tests in English, maths and ICT and many seem to be struggling.

Exam boards revealed that the tests had been a major reason for more than a quarter of pupils failing to achieve a grade in the first high-level Diplomas.

It is a problem picked up at Ashfield School, where pupils who achieved A* in ICT repeatedly failed the corresponding functional skills test.

“Students are struggling to deal with the type of question and examination style in these tests,” said Mr Davies. “They are not used to being tested more on application than knowledge. Students might not recognise the skill they are being tested on even though they possess it.”

The results also highlighted a bizarre grading system that only sees A*-B grades available for pupils taking the foundation-level Diplomas. Then there is the fact that the compulsory work-experience element does not need to be in a relevant industry and that you can actually fail the core “principal learning” content of a Diploma and still gain an overall pass.

All these problems, combined with their belief that the qualification has been mis-sold to the wrong audience, have convinced the Conservatives that change is needed. But even if they decided it could continue after a few tweaks, its long-term future would remain in huge doubt under the Tories because of the party’s plans to reform school accountability.

It wants to end the practice of vocational qualifications being given A-level and GCSE equivalences - at the moment an advanced Diploma is worth three and a half A-levels in the performance tables and an extended advanced Diploma four and a half. The Tory team is concerned that too many pupils end up taking unsuitable courses simply because it helps their school climb the tables.

It says that their proposals have been misrepresented because they would not lead to separate academic and vocational tables, merely see qualifications being judged on their own merit. But the fact remains that the media is likely to continue to compare schools and compile tables based on A-level and GCSE results. Any attempt to decouple vocational qualifications from these headline measures would, according to John Dunford, Association of School and College Leaders general secretary, “kill the Diploma overnight”.

So unless Labour stages a remarkable electoral comeback, the future for the Diploma looks bleak. Instead of the end of the academic vocational divide envisaged by Tomlinson, it could well become a short-lived footnote in history, a monument to what happens when political concerns are allowed to overrule the educational.