This situation is likely to get worse and not only because, as the college points out, 45 per cent of heads are due to retire in the next decade. The college’s own national professional qualification for headteachers, mandatory since April, will also limit the candidates available. Yet its research tells us nothing about whether there will be sufficient numbers of qualified candidates willing and able to fill the vacancies.

What effect, for instance, will the fact that the profession is becoming overwhelmingly female have on teachers’ willingness to train for headship on top of other commitments? And how ready will they be to move home and families to fill vacancies wherever they occur?

The NCSL solution to the shortage of heads seems to involve distributing responsibilities more widely in schools. A refreshingly independent stance, perhaps, but somewhat at odds with recent steps taken by the Government to abolish management points in order to force scarce teachers to concentrate on teaching rather than management.

The college is not the only official agency showing a distinct lack of joined-up thinking about the avalanche of head and teacher retirements that will hit schools as the remaining post-war baby-boomers bow out. This is likely to produce staff shortages unprecedented not only in scale but also in distribution.

The schools and authorities hardest hit will necessarily be those which until now have enjoyed the most stable staffing - those with little or no experience of serious recruitment problems. For once teacher shortage hotspots in the south east and London may be less affected immediately since their staff are generally much younger.