When chief inspector Chris Woodhead last faced the Commons education select committee in February, Margaret Hodge and her fellow MPs gave him a roasting.

This week, as the cross-party committee launched its full-scale inquiry into the inspection service, the MPs were without a leader.

Mrs Hodge has relinquished her position since promotion to education minister, and it was left to temporary chair Charlotte Atkins to introduce the committee’s first witnesses.

Despite teachers’ near-universal hostility to the Office for Standards in Education, a joint report by researchers from Reading University and London University’s Institute of Education found inspections had brought benefits .

But the investigation, based on studies of inspections since 1994, also found the quality of many of them wanting. “We and others have uncovered too many examples of poor practice from individual inspectors,” said the report.

The authors called for inspectors to undergo annual retraining, and said heads found the key issues in OFSTED reports useful for school development.

It said there were dangers, perhaps greatest for schools most in need of help. Confident schools benefited from “free consultancy” but those which lacked confidence were undermined. The notice period remained too long, ratcheting up stress, and leading to over-preparation.

The research team quoted OFSTED’s own research last year that inspectors disagreed on the quality of unsatisfactory teachers in as many as one-third of cases.

They said many inspectors lacked credibility to teachers - because they had taught different ages or subjects, or demonstrated glaring incompetence. But schools were afraid to complain.

Inspectors should get the same five days a year in-service training that teachers receive, the team told MPs - particularly as OFSTED reports depended so heavily on value judgments.

“For some of them, their training was five or six years ago. To keep their reliability and validity they need to be regularly retrained,” said Dr Janet Ousten, of the Institute of Education.

There were worrying signs that OFSTED was becoming an orthodoxy, with schools having to follow the inspection handbook, increasing conformity and removing diversity. Every school was individual but there was a danger teachers were abdicating their professional responsibility to make decisions.

The committee will publish its report into the role of headteachers next week. The OFSTED inquiry will take the committee several months and Chris Woodhead will have to wait until next spring for his grilling.

“The Work of OFSTED”, Brian Fidler, University of Reading, Janet Ousten, Peter Earley, Neil Ferguson, Jackie Davies, Institute of Education, London University.

Document of the week, page 21