The Department for Education and Skills is to trial a new measure for 500 secondaries in this year’s tables. It will reveal, for each subject, what proportion of pupils achieved a grade C or better at GCSE or a level two in key and basic skills.

The move comes amid continuing controversy over many schools’ use of general national vocational qualifications, deemed to be worth four GCSEs at grade C or better, to improve their league table positions.

Schools have previously been judged on the proportion of pupils achieving five A* to Cs at GCSE, in any subject, or through “equivalent” qualifications, such as the intermediate GNVQ.

Analyses by The TES and by David Brown, a former headteacher, have revealed that many secondaries in the Government’s list of England’s most improved schools owe much of their position to the use of GNVQs.

Sir Mike Tomlinson, in his two-year review of secondary qualifications, also said league tables should put more emphasis on English and maths.

The Government announced in a white paper in February that it planned to trial a new measure, which would rank schools on the proportion of pupils achieving five A* to Cs at GCSE or equivalent, including English and maths.

The new indicator would go further, allowing the public to scrutinise results in these two subjects alone. If the statistic became the key way of ranking schools, secondaries would have no league-table incentive to put pupils on GNVQ courses.

Under the trial, results for the proportion of pupils achieving grade C or better in English and maths GCSEs will be released to all schools and local authorities this winter.

Four other indicators, among them the percentage of pupils gaining five or more GCSEs including English and maths, will also be given to schools and councils. The DfES will publish these indicators for 500 pilot schools separately. Ministers will then decide which measures to use in tables for all schools in 2006.