Speaking at a conference in London organised by the National Union of Teachers and the Demos think-tank, Mr Woodhead said that schools were not always able to identify their own weaknesses.

Chris Woodhead says that schools need external inspectors

"It is being suggested that the judgements of teachers and those of inspectors are equally valid. Inspectors get things wrong, but so do teachers.

"But to compare the legitimacy of inspectors' judgements and those of teachers seems to me to be utterly nonsensical."

Mr Woodhead was responding to calls by the NUT's General Secretary, Doug McAvoy, that the current inspection system should be replaced by methods less likely to leave teachers with such a sense of "deep apprehension".

"Teachers consider inspections as something similar to the hurricane season," said Mr McAvoy.

Charles Clarke wants evaluation to lead to action

The conference, which considered how schools should be evaluated, was earlier addressed by Schools Minister Charles Clarke.

Mr Clarke told the conference that schools must set themselves more rigorous targets, arguing that tougher self-assessment would drive up exam results and reduce truancy.

"The recent Ofsted report on self-evaluation indicates that many past evaluation systems have been too weak," Mr Clarke said.

As well as raising targets, the minister said that schools should follow examples of good practice "which make sure that evaluation leads to action".

"Schools must ensure self-evaluation tackles the most stubborn problems - pupil absenteeism and the gap between the achievements of boys and girls, for example."

But the setting up of self-assessment systems would not mean the removal of external inspections, the minister emphasised.

"All the professions, including teaching, must realise that the days when they could just be accountable to themselves are long gone," he said.

"School performance matters to the public; they want to know when and where schools and individuals are struggling, and if we know these things about a school we can intervene quickly."