Colin Richards, who was the primary-sector specialist adviser at the Office for Standards in Education until the end of last month, attacks the way Mr Woodhead presents evidence from inspections in his most recent annual report.

In an article in today’s TES, Mr Richards says that Mr Woodhead’s “politically-inspired negative comment” and “highly economical use of registered inspectors’ judgments” is giving the public a misleadingly gloomy picture of primary teaching and is contributing to the sector’s “deep malaise”.

The attack is likely to embarrass Mr Woodhead both because of the seriousness of the allegations and because it is the first time he has been criticised publicly by a former senior member of his own staff.

Mr Richards, speaking to The TES this week, says that there are marked differences in the way data was interpreted in last year’s annual report compared with this year’s. He takes issue with Mr Woodhead’s use of the scale against which general aspects of a school’s performance in, for example, assessment, are judged. The scale runs from one to seven and, in previous years, Mr Richards says, the mid-point, four, was treated neutrally. “This year, Chris Woodhead decided that ‘four’ means ‘in need of improvement’. ”

This, says Mr Richards, is how Chris Woodhead was able to come up with the statement that half of all primary schools are unsatisfactory.

But next year the mid-point is to be regarded as positive, so in next year’s annual report there could be an apparent dramatic improvement - just before the general election.

Mr Richards also singles out paragraph 48 of the chief inspector’s annual report, which talks about standards in core skills. This presents the evidence in a “laughably negative” way, saying that writing skills are poor in a fifth of schools at key stages 2 and 3, but failing to mention what they are like in the other four fifths. “He should show the data and say ‘this is a personal interpretation’.”

Mr Richards also asserts that the “old established values” of HM inspectors are at risk. “OFSTED is now an arm of central Government, enforcing policy rather than evaluating effects . . . my concern is that through the use of OFSTED’s database, a partial picture of primary education is being presented. ” He says that primary education is in danger of being driven back into a crude 19th-century approach.

Neither OFSTED nor Mr Woodhead were prepared to comment on the allegations.

Two other recently-departed senior HM inspectors back up Mr Richards’ views, but prefer to remain anonymous. One says that Mr Richards’ worries are “almost universal” among the inspectorate. He accuses Mr Woodhead of “politicising the agenda” and employing a “double-the-number-you-first-thought-of” approach to statistical evidence, in particular the statement that 15,000 teachers are inadequate.

“Chris Woodhead is a decisive character and we welcomed the fact that he spoke out, but he doesn’t listen. He’s demeaning the office of chief inspector. ” He also accuses Mr Woodhead of suppressing a report on methods of tackling failing schools in America, “because it called into question the Government’s approach”.

The other former HMI says that the inspectorate was disturbed by the report on class size last year “based on inspections which were not designed to determine whether or not class size made a difference”.

He also complains that Chris Woodhead regularly meets right-wingers such as Sheila Lawlor and Baroness Blatch, but only occasionally with Labour’s David Blunkett and the other side.