The independent sector has been accused of rubbishing the new 14-19 diplomas. We have been critical but, in our defence, the diplomas as currently designed threaten many of the aspects of education that we independents hold most dear. Is it any wonder then that when Ed Balls predicts diplomas will become the only show in town - or, in his words, “the qualification of choice” - we fear the worst?

We are worried about academic challenge being diluted by the emphasis on vocational education. The five diplomas already underway - creative and media; construction and the built environment; engineering; information technology; and society, health and development - are practically based. That is fine for those who want to follow the vocational route, but it should not be forced on those suited to a purely academic diet.

A recent comment by Jim Knight, the schools minister, only fuelled our fears: “They’re not vocational qualifications, but a mix of theoretical and work-based learning that will break the old divide between academic and vocational learning.”

Only a tiny minority of independent schools are super-selective, but all are concerned that diplomas might reduce the academic challenge for the most able. At the same time, those who would welcome really good vocational routes are discouraged by the sheer complexity of diplomas.

The Government encourages schools to collaborate - a sensible move - but sharing the delivery of post-14 programmes requires schools to sacrifice individuality of provision to create common timetables. This may bring other, compensating benefits - including a greatly increased curriculum offer - but independents are, well, independent. We are defined above all by the ability to go our own way, so such a surrender is unacceptable.

From the sidelines, we have seen how a consortium’s painstaking planning can easily be frustrated by basic but predictable failings of infrastructure. I have heard woeful tales from students who suffered from buses regularly failing to turn up or found their appearance mocked on travelling from a non-uniform-wearing sixth form to another that retained uniform. Some end up repeating the year at an independent school or leaving school altogether. Too many loose linkages; too many things to go wrong.

Obligatory work experience is another worry for us. We all send students on work placements. It gives them a (fairly superficial) taste of a possible career. Nor does it hurt them to practise turning up smartly dressed and on time. But diplomas demand subject-related work experience: potential engineers are required to spend time in engineering.

In truth, if that could be done well, it might be fine: students get a lot out of the established Engineering Education Scheme that links them with manufacturers. But if we really want to produce world-class engineers, sixth formers need to do a lot of work at “hard” subjects, including maths and physics. Ironically, although the UK is not producing enough engineers, winning places at the top engineering universities is incredibly competitive. Candidates need top grades, and must work like fury to get them. Significant time spent away from academic study will damage their chances.

Moreover, any teacher who has arranged work experience will have quickly learnt that, one, a nervous breakdown lay just around the corner because, two, it is a logistical nightmare.

The Government proudly announced that the Confederation of British Industry was behind diplomas. Its ardour has since cooled. Perhaps employers realised that they simply could not provide work experience on the scale politicians envisaged.

So what would make the independent sector jump at diplomas? We would require a structure that:

- allows seriously academic pupils to be seriously academic;

- doesn’t dress up vocational routes as something spuriously academic;

- allows a well-defined “mix of theoretical and work-based learning” for those who want it, but clearly differentiates between the two;

- permits candidates to choose programmes of study that match their intellectual and vocational needs, rather than being driven by a bureaucratic assessment process or an obsession with enforcing breadth;

- allows a single institution to teach the qualification; does not require work placements;

- is recognised by all universities, as well as employers, as a mainstream admission route to even the most selective degree courses; and

- ensures that the extended project is intellectually challenging.

Ah, yes, the extended project. In general, independents love the idea, as long as universities take it seriously and Ofqual does not allow it to be watered down. It must involve university-style high-quality research where the process, preparation, methods and final presentation are all rigorously assessed. Worthy, thorough, yet dull verbiage must not gain high marks. To meet the challenge of the extended project, schools will have to teach learning, research and reporting skills earlier and on a scale never achieved before. That would be a huge step forward.

So, keep the project pure and make diplomas simple, flexible and demanding. Then, who knows?, we might find both sectors working towards a common qualification, surely the best outcome for all.

The views expressed are personal.

Dr Bernard Trafford, Head of the Royal Grammar School, Newcastle upon Tyne, and vice-chair of the Headmasters’ and Headmistresses’ Conference.