Sandra Morton, the acting head of Impington Village College, in Cambridgeshire, said that ministers had been forced to act because the "gold standard" exam had lost its lustre among universities. The danger was that A-levels would now be seen as a second class qualification, she said, a split which Mr Blair could have averted had he accepted the Tomlinson report recommendations.
Baccalaureate students have to select one subject from each of six subject groups, covering English, foreign languages, science, humanities, mathscomputing and the arts. They have to complete an extended essay, a "theory of knowledge" philosophy course, a community service unit and also make an oral presentation to their peers.
Impington has offered the IB and A-levels for the past 15 years. Mrs Morton said the Government's decision was a welcome acknowledgement of the strengths of the IB, but added: "The danger is that the IB will be seen as the prestigious academic pathway and the A-level as an also-ran."
John Dunford, the general secretary of the Association of School and College Leaders, said any support for the baccalaureate was not a comment on the A-level: they were simply different qualifications.
In today's TES, Mr Blair says: "If we are serious about tailoring education to the needs of young people, they should have real choices after 14 - strong qualifications with strengthened A-levels, new diplomas, the IB and apprenticeships. These choices will to help meet the needs of young people, the demands of industry and the requirements of universities."
David Willetts, the Shadow Education Secretary, said that all students should be able to study the IB and the International GCSE.
Pressure for change has been intensified as leading private schools, including Eton, have banded together with Cambridge University's exam board to produce a more traditional A-level style exam: the pre-U.
Offering the IB is not cheap. Schools must pay pound;3,000 to pound;4,000 a year in fees. The Government has said it will meet this cost.
Tony Blair writes, page 26