A couple of years ago, a state school teacher got in touch with me with concerns about the Cambridge Pre-U exam, an alternative to A-levels introduced in 2008. She was worried both that it gave yet another unfair advantage to privately educated children, and that it involved potential conflicts of interest, since many of the questions were set by teachers whose pupils would be taking the exams. In a piece for Independent School Parent (what you do mean, you don't subscribe?) in 2012, the headmaster of Winchester College explained why the school had dropped A-levels in favour of the Cambridge Pre-U:

About seven years ago, a number of heads of independent schools (myself included), approached Cambridge International Examinations (CIE), with the proposal that they might develop an alternative to A level, to restore the measure, content and rigour characteristic of A levels 25 years ago, before the aggressive programme of successive governments to increase access to universities inevitably compromised intellectual quality. In response, CIE developed the Cambridge Pre-U. Winchester adopted the course in 2008.

Writing in the Telegraph in 2008, the 'high master' of St Paul's School explained why he wasn't adopting the Pre-U. One of his reasons was that he was worried it would 'widen the gap between the two sectors' (i.e. between the institutions referred to euphemistically as 'independent' and 'maintained' schools), because 'the maintained sector simply does not have enough graduate maths, science and modern language teachers to deliver the Pre-U.' In passing, he mentioned that 'Winchester College has held a leading role in the birth of the Pre-U', and then referred to it as 'the Pre-U that Winchester has backed so heavily'.

In 2010, the school announced that 'nearly a fifth of the Winchester candidature secured a D1 grade, which is rated above the new A* grade at A-level.' One of the things this means is that, as intended, pupils taking the Pre-U can claim to be better than A*, which pupils taking A-levels can't, however brilliant they may be. This seems on the face of it unfair.

'Of the 150 schools who made entries for Cambridge Pre-U in 2014-15,' a spokesperson for CIE told me, ‘65 are independent schools, 60 are state schools, and the remainder are "unknown" – some schools overseas do not clearly sit in either category. Of the 150, 32 are outside the UK.' Only around 18 per cent of pupils over the age of 16 are privately educated; the private sector is therefore over-represented among Pre-U schools. But CIE denied that the exam discriminated against state school pupils: 'We invested substantial time and money in submitting Cambridge Pre-U qualifications for Ofqual accreditation so that students from state schools could access them and state schools are well-represented in both uptake and entry numbers.'

On 3 August this year, the headmaster of Eton [*] wrote to his pupils with the news that Mo Tanweer, the head of economics at the school and a principal examiner for Pre-U economics, had 'left Eton's employment' after it was discovered that he had breached exam security by sharing 'practice questions' with his colleagues at the school. 'There is no suggestion that any boy at Eton has done anything wrong, nor is any member of staff other than Mr Tanweer implicated.'

It then emerged that Winchester had suspended its head of art history, Laurence Wolff, for giving pupils 'prior information on exam questions'. Wolff, too, was a Pre-U examiner. He has now retired from the school. Once again, no pupils and no other teachers are said to have done anything wrong.

Meanwhile, Charterhouse has also been under investigation for Pre-U shenanigans. But these are all isolated incidents.

Mr Wolff, as I knew him when he taught me 25 years ago, was one of the kindest teachers at Winchester. In some ways, the worst that can be said of the misdemeanour that cost him his job, wrong though it plainly was, is that he was being too kind to his pupils. And whatever unfair edge he was giving them – now negated – seems trivial next to the massive advantages already bestowed on them as pupils at a 'prestigious public school'; sneaking a peek at an exam paper pales next to the entrenched inequalities perpetuated by England's 'two sector' education system.

In my day, as well as teaching art Mr Wolff organised the community service programme for boys who didn't want to spend Wednesday afternoons playing at soldiers. He once sent us out knocking on doors to collect money for Barnado's. One old man looked at the collection tin in my hand, looked at me and said: 'You aren't one of those boys, are you.' He shut the door before I could explain the money wasn't for me, as if he didn't already know that.

The scraps of largesse that private schools bestow on the less fortunate are among the reasons that allow them to continue to be classed as charities, with all the tax benefits that charitable status brings. Fees at Winchester are now well north of £30,000 a year. The median household income in the UK is less than £27,000. Funding for state schools has steadily declined since 2010; they have been forced to lose teachers, teaching hours and entire subjects to make ends meet.

[*] Full disclosure: Eton's headmaster, Simon Henderson, was a contemporary of mine at Winchester. Haven't we done well for ourselves.