The letter, a copy of which has been passed to The TES, is signed by the heads of three schools in the London borough of Wandsworth and one in Hampshire. They describe a “disturbing pattern of common features” during their inspections and include a selection of bizarre remarks allegedly made by the inspector, Geoffrey Owen.

The heads also raise questions about the accountability of inspectors, arguing that the complaints procedure of the Office for Standards in Education is “totally internal”, and occurs after a school’s local reputation has been damaged.

Of the four, the only school to be failed by Mr Owen was Hillbrook, a grant-maintained primary in Wandsworth. The head, John Harries, says that the appalling report the school received last autumn was totally unexpected. “We didn’t expect to escape criticism, but we hoped for a cool outside analysis of strengths and weaknesses. Instead we were comprehensively rubbished. The stuffing was kicked out of the place.” Mr Harries claims that after delivering his verdict, Mr Owen said: “It is cruel, but that is the OFSTED way.”

The corroborative visit by HMI, however, failed to confirm that the school was failing. It is, according to OFSTED, very unusual for a registered inspector’s report to be overturned - a spokesman said that it had happened on fewer than five occasions.

Mr Harries said he felt emotionally destroyed by the experience and was off work for a month. When he returned, he was contacted by the two other Wandsworth primaries and, through a chance encounter, by South View school in Hampshire - all of which had been inspected by Mr Owen’s team. While the other schools had all passed their inspections, staff felt that their reports did not reflect the strengths or weaknesses of the schools and they have requested visits by HMI to corroborate the registered inspector’s report (this only happens automatically after a school is deemed to need “special measures”).

According to the letter, Mr Owen warned the head of Earlsfield school at the start of the inspection that he had failed three schools already. At the post-inspection meeting, he told staff: “If you people think that this is a good school, I am here to tell you differently”.

At South View, head Angela King said that on the last day of inspection Mr Owen said: “I have failed schools with the evidence I now have before me”. But Mr Owen did not fail South View, which, say the heads, brings into question the consistency of his judgment and the appropriateness of his comments.

At Hillbrook, the head said Mr Owen promised that the school would receive “the Rolls-Royce of inspections”, adding that this would be “no consolation to those crushed beneath the wheels”.

The heads complain that during the inspections Mr Owen expressed personal views on subjects such as appraisal, mixed-age classes and topic work, “suggesting an element of prejudgment”.

The letter says that parents at Earlsfield believed Mr Owen was encouraging them to make negative statements and describes how the head of South View felt when Mr Owen advised her to go to WH Smith and buy a copy of the national curriculum. The reports were all “relentlessly negative” and contained “serious internal contradictions” say the heads. Peter Coles, Hampshire’s chief education officer, has written independently to Chris Woodhead complaining about the treatment meted out to South View and another Hampshire school.

Eric Poppitt, Hampshire’s assistant CEO, said that Mr Owen failed to back his conclusions with hard evidence during the feedback meeting to governors, and that the team seemed determined to seek out negative aspects. “There’s no way Hampshire would want to defend a school that is not providing proper service, but we believe South View is doing a good job in a difficult area and that the report took no account of this. The damage to staff morale has been enormous. ”

In Somerset, deputy CEO John Freeman told The TES that one of the county’s primary schools had been inspected by Mr Owen in November 1994. “We were surprised when the school was found to be in need of special measures.” The CEO, he said, wrote to OFSTED twice, questioning the evidence base for the report. In particular, he questioned whether the inspection “fitted in with the OFSTED statement ‘improvement through inspection’.”

A spokesman for OFSTED confirmed that Mr Woodhead had received the letter from the four heads and that the complaint would be considered by the team that deals with registered inspectors. He said it is quite possible for a registered inspector to be struck off, either for gross misconduct or for producing reports that do not give an accurate or fair reflection of the schools.

“We have not struck anyone off yet, although a handful of inspectors have jumped before they were pushed - once they realised they were being investigated.” He said that there had only been five or six cases so far. “We have 1,200 RgIs; some will be better than others.”

Mr Owen is a secondary mathematics teacher, employed as an inspector by Cambridge Educational Associates. The managing director of CEA, Brian Oakley Smith, said he could not comment on any aspect of Mr Owen’s past or present work and that Mr Owen was prevented from commenting under OFSTED’s code of practice.