“Old mathematicians never die,” runs the old joke, “they just lose some of their functions.”

If it is also true that mathematics is 50 per cent formulas, 50 per cent proof, and 50 per cent imagination, let’s briefly imagine a different approach to English and maths.

Are we all agreed that these are the two most important subjects? Someone at the Department for Children, Schools and Families clearly thinks so because the measurement of schools by the percentage of pupils gaining five GCSE grade Cs or higher with English and maths is now the only significant indicator of a school’s success.

My guess is that this reflects what a lot of people think: that being able to “do” English and maths is perceived as an essential skill for life. The only nay-sayers may be a gloomy cohort of Year 11 CD borderline students who already feel ground down by the sheer volume of booster classes and mentoring sessions they are being subjected to.

Whatever your political persuasion - whether a Goveist blazer-defender or a Ballsite diploma promoter - the need to gain a grade C in these two core subjects is likely to be seen as a Very Good Thing.

It is interesting how little we hear the politically unthinkable - that maths beyond the age of 14 may be rather less important than we assume. After all, how much maths have you used today? And of that, how much is actually stuff that we should have mastered by the age of 14 anyway - working out how much time to leave for a journey, calculating the shared cost of a meal out with friends, or estimating how big a shock our monthly credit card bill might prove to be?

And is it the same with English? Might the relentless GCSE diet of poetry and those fatuous examination-writing questions do more harm than good? “Describe the room you are sitting in,” was one GCSE task issued to the thousands of pupils sitting in bleak sports halls last summer. Don’t some of our pupils end up thinking they hate poetry and can’t write because of such an unappealing curricular diet?

The educational argument for removing English and maths from the compulsory curriculum is that some pupils would benefit from a genuinely vocational experience, the kind of thing now being vaunted in the Conservatives’ plans for technical schools. These pupils would presumably have to demonstrate their functional skills in numeracy and literacy, but not by taking a GCSE qualification.

Then there is the social argument - the recognition that in an age of technology, we use maths less than we did in the past.

There is also the pragmatic argument: with many schools facing an ongoing chronic shortage of high-quality English and maths teachers, wouldn’t the quality of teaching, the motivation of pupils, and the net impact on educational standards improve?

Or am I merely ensuring that sales of my English textbooks plummet and I get deleted from the Christmas card lists of maths teachers?

The idea that any politician would propose that English and maths should no longer be compulsory beyond 14 seems pretty unthinkable. Yet it must have been the original - rather understated - thinking behind developing functional skills so that students on diploma and other pathways would notch up their achievement in literacy and numeracy in other ways.

This struck some of us as eminently sensible, creating the curriculum space for a genuinely flexible and personalised provision. It would also enable us to put right the black hole of key stage 3, developing courses to ensure that every pupil experienced a motivating, engaging and relevant educational entitlement that prepared them for the specialisation of the 14-19 curriculum.

Instead, the ground has shifted. September training days used to be a time for a staff’s collective celebration and dissection of the school’s summer GCSE results. But the spotlight on English and maths colleagues, and the heavy weight of accountability on those subject leaders, is changing that. After all, you could be the best school in the universe and then get hit by a succession of staffing issues in one of your core subjects - sickness, stress, disciplinary action, maternity leave - and suddenly, almost literally, that major blip in English or maths could leave you stranded helplessly in an Ofsted “category”.

In a medium-size school, the difference between outstanding and inadequate attainment may prove to be merely a dozen students gaining or missing their grade C. And with inspectors instructed to place more emphasis on attainment - raw scores rather than value-added progress - the stakes have never been higher.

So no wonder we are all busily tracking our “key marginals” - the pupils who look like they will not get a C in English (often boys) or maths (often girls) - and devising a programme of intervention activities that makes William Beveridge’s plans for a national health service look timid.

It is what happens when the measures to assess pupil progress are also used to judge and categorise schools, catapulting some to the stellar heights of premier league status while others topple unwittingly into special measures.

It is proving a policy with unexpected consequences that perhaps do not quite add up.

• Geoff Barton, Headteacher, King Edward VI School, Bury St Edmunds.