Leading article: An overhaul of the exam system is long overdue

The investigation into Britain's examination system instigated by the Education Secretary yesterday comes not a moment before time. The extent to which examiners have been tipping off teachers about future test questions is just the latest, and most shocking, evidence of a broken system that demands immediate attention.

That said, the latest revelations should not have come as a surprise. Charges against exam boards are not new. Neither do the critics lack credibility. In a book published last summer, for example, Mick Waters – one of the country's most senior examination advisers and a former director of the body responsible for devising the national curriculum – accused boards of no less than "insider dealing" and claimed that the A-level and GCSE testing system in Britain was "diseased" and "almost corrupt". Strong stuff, indeed. It is regrettable that Mr Waters's concerns were not heeded earlier.

The nub of the problem is the structure of the system itself. The incentives are all wrong. On one side are the four main exam boards which compete for business from schools: the Assessment and Qualifications Alliance; Edexcel; the Oxford Cambridge and Royal Society of Arts; and the Welsh Joint Education Committee. On the other are teachers who are desperate to enhance their league-table ranking by improving exam results, and are threatened with "interventions", including the sacking of the headteacher or closing of the school, if they do not.

Put the two together and it is almost inevitable that they will collaborate. And, it seems, they have. The seminars and conferences ostensibly convened to explain the syllabus have too often become a forum for passing on tips about next year's exam questions. Exam boards' relationships with publishing firms – which enable them to make a profit from selling text books, often written by their chief examiners and including examiners' tips – only muddy the waters even further.

Michael Gove has given Ofqual two weeks to look into the charges of impropriety and to work up some possible solutions. There is one that immediately stands out. The Education Secretary must put an end to the distorted market of multiple, commercial exam boards, replacing them with a single organisation to serve the country as a whole.

A national exam board would, at a stroke, eliminate any reason for examiners to curry favours with schools. And, by removing the incentive for boards to hint to headteachers that their tests may be easier, it might also address perennial concerns that exams are being "dumbed down" to boost grades.

In fairness to Mr Gove, he has made some progress in this area since taking on the education brief. Some specific issues – such as an over-reliance on coursework, or the ability of candidates to take repeated resits to boost their grades – are being tackled. Coursework will be taken out of GCSEs over the next two years, for example. Mr Gove has also said that he would like to see more university involvement in the setting of exam questions.

So far, so good. But only a major, structural overhaul of the exam board system as a whole can hope to address a fundamental malaise that encourages teachers and examiners to game the system, to the detriment of pupils' educational standards.

Mr Gove's ideological instincts no doubt favour reliance on market forces in all aspects of the education sector. There are, arguably, parts of the system where such an approach has merits. But national examinations is not one of them. The basic premise of exams is that they act as a taxing standard against which all are tested equally. For too long they have been anything but. Mr Gove must be brave enough to remedy the situation.