The tests, proposed in March as a surprise addition to a package of A-level reforms, aim to stretch the most able candidates and enable top universities to choose between pupils with equally good grades.

Education minister Baroness Blackstone intends to introduce the tests in all major “academic” A-level subjects after previous plans to limit them to six subjects were condemned by heads.

Ministers intend to launch two more exams, for able nine and 13-year-olds. All three will be known as world-class tests, although the sixth-form version will be formally titled the Advanced Extension or AE exam.

There will be no Extension level in business studies even though it was the eighth most popular at A-level this summer.

Baroness Blackstone believes the new Extension level must remain essentially academic in nature and that its purpose - to select candidates for leading universities - could be undermined by including vocational subjects.

The Government’s exam quango, the Qualifications and Curriculum Authority, initially proposed that the tests be introduced in six subjects: English, maths, chemistry, physics, history and French. However, headteachers argued this would be unfair to able candidates who would be unable to take the exam in their strongest subject.

Baroness Blackstone has now agreed that the tests will also be developed in biology and geography, which have sizeable A-level entries, as well as in economics, religious studies, German, Spanish and Latin.

Plans to develop tests in classical Greek and critical thinking have been put on hold. The QCA plans to trial a limited number of tests next summer and intends to introduce them nationally in 2002.

John Dunford, general secretary of the Secondary Heads’ Association which condemned the original proposals to limit the number of tests for 18-year-olds, said: “Extending the number of tests will be much fairer, give more pupils the opportunity to take them and make it less likely that individual universities will develop their own tests.

“However, the tests will undermine the thrust of the Government’s A-level reform by narrowing the sixth-form curriculum. I am concerned that pupils may spend all their time concentrating on taking a world-class test rather than, say, taking up a language and broadening their study.”

The tests will be externally assessed, usually by a written exam, although dissertations and coursework are being considered. They will be based on the general A-level subject criteria rather than on individual syllabuses and will require greater depth of understanding rather than greater breadth of knowledge.

The papers for sixth-formers will be marked as distinction, merit or ungraded.

The tests for nine and 13 year-olds were announced as part of the Government’s “Excellence in Cities” initiative to raise standards in inner-city schools and provide for the gifted and talented pupils. Children will use computers for at least part of the tests in maths and problem solving.

Only the brightest pupils will take the demanding but voluntary tests which will give the top 5-10 per cent access to university summer schools and masterclasses at specialist and private schools.

The QCA has already advertised for test agencies to tender for contracts to develop these tests. The contract will be awarded next month.