The decision by Colin Richards to join the exodus of senior HM inspectors from the organisation may have removed a thorn from the side of the chief inspector, but has allowed the former specialist adviser on primary education to launch an unprecedented attack on his former boss.

In the normal order of things, Mr Richards would have been expected to take charge of the primary HM team as part of the re-structuring within OFSTED. However, Mr Richards was informed by Mr Woodhead, the chief inspector, that he wanted a fresh look taken at primary education. Another senior job was offered and refused.

The events prompted Mr Richards to take the distinctly un-HMI action of placing his criticism in the public domain. After 13 years in a service renowned for producing considered, if ponderous, reports on schools, Mr Richards has broken ranks in the most forthright terms.

The case as made by Mr Richards is that Mr Woodhead has painted a picture of primary schools as dismal places where children are not effectively taught to read and write. And what makes the accusation serious for Mr Woodhead’s position is that Mr Richards claims the chief inspector misused the data that have been collected from school inspections.

The culture within the HM inspectorate - while the organisation changed its name to OFSTED, the inspectors retained their title - is that any judgment on schools has to be backed with evidence. Almost since the arrival of Mr Woodhead there has been insistent whisperings of discontent at what some HMI perceive to be cavalier use of evidence by the chief inspector.

There is a view that Mr Woodhead’s calculation that there are 15,000 bad teachers in the system is based on dodgy calculations of the number of poor lessons observed during inspections. There are cynics who suggest that OFSTED’s finding that the size of classes is not linked to effective teaching is politically convenient.

The concern of Mr Richards is primary schools, and academics attest to his expertise and believe his departure will be a genuine loss to the service. He was one of that rare breed of graduates who started their career teaching in primary schools. Before being seconded to HMI in 1983, he trained and supervised student primary teachers.

Within HMI he was rapidly promoted, taking charge of curriculum issues in both primary and secondary schools, and latterly becoming specialist primary adviser. It is only in the past two or three years that he has become a major internal critic of OFSTED.

In part, the quarrel with Mr Woodhead is about fundamental issues around the state and nature of primary schools. Mr Richards argues that while schools are probably devoting enough time to the basics of reading, writing and numeracy, it may be that they could use that time more effectively. He doesn’t want to see other subjects squeezed out of primary schoools in order that more time is spent on the basics.

In part, it is a falling out over style and presentation and, on Mr Richards’ side, a growing grievance at having his expertise ignored. No doubt, Mr Woodhead views his former inspector as part of some liberal Romantic movement resisting a return to greater structure in primary classes. Certainly, Mr Richards does not share Mr Woodhead’s enthusiasm for whole-class teaching, but he does argue that primary teachers could usefully spend more time instructing the whole class.

However, Mr Woodhead may have problems dismissing Mr Richards as a disgruntled inspector out to get revenge. Other staff have left making clear their disillusion with OFSTED, and Mr Woodhead in particular, but not publicly.

Nor may Mr Woodhead be able to shrug off easily accusations of using data to produce a misleading report on the state of primary education. The question is why would Mr Woodhead want us to believe primary schools are worse than they actually are.