The igcse will never replace conventional GCSEs as the main state school exam of choice, according to the board that developed the O level-style qualification.
The decision to allow state schools to start teaching for the more traditional exams in all subjects from September, revealed by The TES last month, was confirmed by ministers this week.
It prompted some reports to suggest that state schools would now abandon conventional GCSEs "no longer seen as fit for purpose".
But University of Cambridge International Examinations (CIE), which first developed the IGCSE for international schools in 1988, said that expectation was wide of the mark.
CI communications manager Geraldine Seymour said there had been a big increase in interest in IGCSEs among state schools following the Government's announcement.
But she added: "We don't think it would ever replace the GCSE. It is simply another option; it is all about choice."
The board expects state schools to start offering IGCSEs in individual subjects rather than across the range, depending on the wishes of individual heads of department.
Ms Seymour said English language and English literature IGCSEs were expected to be the most popular, followed by physics, chemistry and biology.
The biggest difference between the IGCSE and the conventional GCSE lies in structure, not content. The IGCSE is linear rather than modular, with no exams in the middle of a course. It has grown in popularity in England's private sector.
More than 90 per cent of the country's top independent schools now offer at least one IGCSE, and some have described it as the sector's "favoured" qualification.
Schools Minister Nick Gibb said this week: "For too long, children in state maintained schools have been unfairly denied the right to study for qualifications such as the IGCSE, which has only served to widen the already vast divide between state and independent schools in this country."
But Ms Seymour said that even in the independent sector most schools offered GCSEs alongside the IGCSE.
John Dunford, Association of School and College Leaders general secretary, said: "GCSEs are well established as the major qualification route and have been hugely successful in giving many more young people the opportunity to achieve.
"There is already confusion about IGCSEs, which are very different from GCSEs and do not meet the same rigorous standard."
The previous Labour government had already approved funding for state schools to offer nine IGCSEs and that has now been extended to the seven exams covering the statutory national curriculum subjects of English, maths, science and ICT.
Exam board Edexcel is also offering a range of IGCSEs currently being considered for accreditation by Ofqual, the exams regulator, which should also be available for teaching from September.
The Government says IGCSEs will be included in league tables "as soon as possible".
It also revealed that, as expected, it will stop funding the development of "academic" Diplomas in science, humanities and languages, which were due to be introduced in September 2011, saving #163;1.77 million.