Bad teachers could be saved from the sack by the very system that is being proposed to identify them, according to heads, inspectors and teaching unions.
They say that the task of identifying the worst staff could distract inspectors from the real purpose of inspection and interfere with the school management. Disciplinary proceedings could also be undermined by inspection judgments based on just one or two lessons.
There are also fears that the potentially time-consuming and expensive changes would threaten the current inspection schedule.
The draft code for inspectors reporting on teachers was issued last month by the Office for Standards in Education to meet John Major's promise that the best and the worst staff would be named.
It requires inspectors who lead the teams to make additional oral and written reports to heads on teachers who are graded either one (excellent) or seven (very poor) under the new seven-point scale. These reports would remain confidential but could be passed to school governors if they request it.
John Sutton, general secretary of the Secondary Heads Association, warned that if a poor teacher tried hard during the inspection and scored more than a seven, this could hamper efforts heads or governors might be making to improve their work. "This innovation will add little to the store of knowledge the school has on individual teachers," said Mr Sutton. "It will demotivate good and aspiring teachers who are not included in the 'grade one' group and could dissipate action being taken against the poor teacher."
Governors who read the reports could be barred from disciplinary proceedings, according to the Association of Metropolitan Authorities, as the inspectors' confidential gradings could compromise their judgment.
SHA also fears that inspections will suffer as a result of the effort involved in the new procedures. It "will skew the planned coverage of the whole school and could lead to a restricted concentration on certain staff. The process will demand that more time is spent on teacher observation than at present and thus increase the length and cost of inspecting."
Keith Anderson, chairman of the Standing Conference of Chief Education Officers, said: "What is proposed will distort the nature of OFSTED inspections."
This view is backed by Margaret Smart, director of the Catholic Education Service and a former chief inspector who said "the proposals shift the inspection away from teaching to teachers themselves".
Neil McIntosh, chief executive of CfBT Education Services, the largest private provider of OFSTED inspections, said its registered inspectors are worried. "We think that inspection is not the proper mechanism to use to manage teacher performance."
Alan Parker, education officer with the Association of Metropolitan Authorities, believes that inspectors will avoid awarding the most extreme grades because of the extra work they generate.
Both SHA and the National Association of Head Teachers have urged OFSTED to adopt a less formal mechanism for reporting on the best and the weakest teachers.
"We are worried about the idea of written reports," said Jeff Holman, an assistant secretary with the NAHT. "It would be much better to have informal discussions between the inspectors and the head. " AMA warned that a teacher judged to be grade seven could be identified in a small school even if he or she were not named. SHA believes that inspectors whose judgments damage a teacher's subsequent career could be open to legal action.
Kay Driver, SHA's assistant general secretary, said: "These proposals will destroy some of the good relationship that has developed between teachers and inspectors. We're not prepared to accept them as they stand."