Schools with "low" raw exam results will be unable to achieve good or outstanding Ofsted inspection verdicts from September, except in "the most exceptional circumstances".
The rule, set out in the details of the watchdog's new inspection framework, applies regardless of the social background of the pupils, their academic progress and the value that the school adds to their achievement.
Schools with "low" raw exam results where the progress made by pupils is no better than satisfactory, and there is little evidence of improvement, will automatically be given a formal notice to improve or be placed in special measures.
Mick Brookes, general secretary of the National Association of Head Teachers, said conversations with senior civil servants led him to believe that the Department for Children, Schools and Families was behind the change.
"This is clearly DCSF policy affecting the way Ofsted inspects in what should be an independent process," he said. "It is unacceptable."
Schools judged to be inadequate - either at promoting equal opportunities among pupils and tackling discrimination or at ensuring pupil safety - are "likely" to be judged inadequate overall and either placed in special measures or given a formal notice to improve.
Ofsted was clear it would be placing greater emphasis on raw results when it announced its new framework earlier this month. But the detail revealed in a separate document, published several days later, may shock the heads of schools serving tougher areas and those with secondary modern intakes.
Christine Gilbert, chief schools inspector, promised that pupils' progress would be considered alongside raw exam results when judging achievement in a school.
But the emphasis on raw attainment will still make it almost impossible for schools with results below a certain level to get a verdict better than satisfactory.
Inspectors have been told "low" attainment should be defined using the National Challenge benchmark of fewer than 30 per cent of pupils gaining five A*-C GCSEs including maths and English, and in schools where final- year exam or test results have been significantly below the national average for three years.
The National Challenge scheme was designed to help schools reach the benchmark but also threatened with closure those that failed to do so by 2011.
Last year, an NUT analysis revealed that of the 638 secondaries then in the scheme, 147 had been judged good by Ofsted and 16 outstanding.
The new inspection framework will prevent the Government being embarrassed by a similar scenario.
John Dunford, general secretary of the Association of School and College Leaders, said the details confirmed his view that the framework would stack the odds even higher against schools in "challenging" areas.
He said it was unreasonable for schools with inadequate safeguarding procedures automatically to be given a notice to improve or be placed in special measures.
Although "crucial", faults in safeguarding were "quite straightforward" to correct, he said, but Ofsted verdicts could damage schools for years.
An Ofsted spokesman said: "When judging the pupils' progress, inspectors take the pupils' starting points into account. Ofsted is an independent body and these changes were proposed in May 2008."