State schools will be able to start offering IGCSE courses in all subjects from September, The TES has learnt.
The Con-Lib commitment to opening up access to the O-level style exams was confirmed last week, but without any indication of timescale.
Government sources have now revealed that the change is among the coalition's priorities and that state schools will be allowed to make the switch to the more traditional qualifications next term.
Pressure has been mounting for the change for several years. More than 90 per cent of top independent schools offer at least one IGCSE, but pupils' efforts have not shown up in league tables because the qualification has not been approved and funded for state schools.
Some secondaries in the maintained sector are also very keen to opt out of conventional GCSEs.
In March, The TES revealed that at least ten state schools were secretly teaching pupils for IGCSEs and planned to enter them privately for the prohibited exams this summer.
Andrew Hutchinson, executive principal at the Parkside Federation in Cambridge, which includes Parkside Community College, is "delighted" at the prospect of being able to offer IGCSE science.
"This will broaden opportunities and choice and close the gap between the state and private sector," he said. "And it really does enhance the science curriculum."
The comprehensive started teaching the science IGCSE syllabus in September 2008 on the advice of its science teachers and governors, who are Cambridge University research scientists.
Parkside added extra sections to the IGCSE syllabus to ensure it matched the national curriculum.
But Mr Hutchinson was unsure about whether this would now continue. "We will wait and see what the greater freedoms they (the Government) talk about schools having will mean in reality," he said.
John Bangs, NUT head of education, said: "We are rapidly descending into incoherence when it comes to exams - with international qualifications treated as being more rigorous than homegrown ones."
Some concessions were made under the previous Labour government, when Ofqual accredited the 16 most popular IGCSEs. In February, ministers said they would fund state schools for nine of the exams, providing they were re-branded as Cambridge International Certificates to prevent confusion with conventional GCSEs.
But the previous government would not fund the remaining seven courses, covering the core statutory subjects of English, maths, science and ICT, because it said they did not meet national curriculum requirements.
Cambridge International Education, the board offering IGCSEs, said it had always been prepared to make teaching Shakespeare compulsory and rejected other claims from the Labour government about the core exams not covering the national curriculum.
See Gove interview, pages 10-11.