Ms Kelly will tell a conference in London that she stands by her decision to retain A-levels and GCSEs and reject the Tomlinson report’s proposal to replace them with an overarching diploma for 14 to 19-year-olds.

She is expected to stress, however, that the Government wants to give greater breadth and stretch to courses for teenagers and will be reviewing qualifications in 2008.

The Department for Education and Skills said there are no plans to scrap A-levels in 2008 and that Ms Kelly’s position is unchanged.

The DfES said that any future diploma, which could include an expansion of the vocational one already planned by the Government, would exist alongside A-levels.

Ken Boston, the chief executive of the Qualifications and Curriculum Authority, was expected to go further in his speech to the conference, which has been organised by the National Association of Head Teachers, the Secondary Heads Association and the Association of Colleges.

Mr Boston said in an interview with the Independent this week that the planned diploma would take over from A-levels as a “natural qualification” within 10 years. “A-levels will be out the door and the diploma will take over,” he said.

A QCA spokesman said that the authority expected that diplomas would become the first choice for students and that they would contain full A-levels and GCSEs within them.

“If we can meet the needs of employers and universities, we have an opportunity to develop a qualification that, in 10 years’ time, could be the natural choice for many students,” he said.

Last year’s report by Sir Mike Tomlinson, former chief inspector, said it would take at least 10 years to introduce a new overarching diploma.

A-levels and GCSEs would be “components which form the building blocks” of the qualification, he said, but would not be available as separate exams.