With the inevitability of the back-to-school stands in Tesco and the first Christmas cards, the annual debate about grade inflation hit us this week as A-level results showed their customary increase in one or all of the performance indicators. “Were you pleased with the exam results?” I once asked a traditionalist colleague. “Well, they weren’t as good as I feared,” came the terse reply.

This year, though, the standard knockabout row has been given a new twist by Michael Gove, shadow schools secretary, who hints that a future Tory government might give more credit to “hard” subjects such as maths and physics, and less to media studies - a subject that my scientist god- daughter, by the way, finds incredibly hard.

The grade inflation debate must mystify foreign commentators: I cannot imagine newspapers in other countries running such headlines as “Baccalaureate gets easier” or “Abitur inflation”. But the debate’s refusal to go away is disturbing. And the answer is not myopically to refuse to acknowledge the issues, as Vernon Coaker, schools minister, predictably does, trotting out the usual line of better results being “a cause for celebration” and that “there has been no dumbing down”.

Of course, the fact that grades at A-level are getting generally higher does not of itself necessarily mean that the exams are easier. As a former principal examiner of French A-level, I can say with confidence that students are self-evidently “better” at some things than those of even a decade ago. They are more ICT-literate, better able to research (although sometimes uncritically), and better at presenting work orally - the linguists speak better, the historians probably argue better. Nor is more professional and better-focused preparation to be ruled out as a factor: how many teachers faced performance management targets in the 1980s?

But when A-levels were invented, the qualification was regarded as a very flexible measurement of ability which allowed universities to distinguish between candidates - a function it no longer fulfils.

An instructive instance of this can be found at Loughborough University, which I visited recently on behalf of the Headmasters’ and Headmistresses’ Conference and the Girls’ Schools Association universities committee. It is a good example of a modern, enlightened university, with a bright, attractive campus, strengths in engineering, design and sport, and graduates who are mostly snapped up by employers. But its ambition is to become a “three As” university. Soon, to study at a good, straightforward English university you will have to achieve what only Oxbridge scholars did two decades ago. For Loughborough, read Surrey, Southampton - and soon, surely, most higher education institutions.

The implication is that all universities are equal, and that AAA is tomorrow’s “A-level pass”.

But even if this were the view of employers (it isn’t) or students themselves (ditto), it isn’t the view of the Government, which relishes HE league tables every bit as much as those for schools.

The exams regulator Ofqual will argue that the level of difficulty is the same in all accredited A-levels. It may be true that a scientist will find media studies no doddle, just as linguists may be mystified by drama. But Geoff Parks, director of admissions at Cambridge University, has published a list of A-level subjects that his institution will not count - the so- called “soft subjects” targeted by the Tories. Mr Parks clearly does not believe all A-levels are equivalent. It is this outright challenge to the received wisdom of A-level parity and the march of student progress that Mr Gove has picked up on this week.

However, the quantity and difficulty of work does not just vary between A- level subjects, but also between specifications. A pupil who studies physics will find it much easier if they take the “advancing physics” A- level course rather than one of the more traditional versions offered by OCR and AQA.

Dumbing down over time can also occur in subjects that politicians might not expect. In A-level English literature, there is little difference between the number of works a student had to study in the 1980s - six or seven - and the number they do now. But in maths, two of the topics pupils would have studied at O-level in 1980 - matrices and vectors - are now part of the A-level syllabus.

All of this would make it very tricky for the Conservatives to draw up a point system for the difficulty levels of different A-level subjects.

If the system does not change, however, teachers in high-performing schools will simply continue to pile the pressure on their students, with A*s, extended projects, fifth subjects, critical thinking courses and so on - all so that they can be stretched more.

While I am not sure Mr Gove is right, his proposals do have a logic to them, and are a sensible opening to a new debate about the difficulty of A-levels.

So I’m happy to assist his research: if he wants to make a start by sitting media studies, and seeing if that really is “soft”, I’m willing to have a go at maths.

• Chris Ramsey, Headmaster of The King’s School, Chester