Ministers then excluded IGCSEs from counting towards school performance tables, which effectively barred state schools from using them.
Cambridge International has written to the chair and chief regulator at Ofqual to rebut claims that IGCSEs are “easier or less robust” than GCSEs.
“Independent schools took Cambridge IGCSE when there was a rumour that they were ‘harder’ than GCSEs,” Mr Parker said in the letter.
“Those same schools continue to take Cambridge IGCSE when there is a rumour they are ‘easier’. Importantly, schools can trust that neither of these rumours is true, as we align our awarding standard with England’s GCSE.”
Earlier this year, research published by Education Datalab showed that two thirds of pupils achieved grade A* and A in IGCSEs in maths and English language, while just 18 to 20 per cent achieved the equivalent grades in reformed GCSEs.
Mr Parker explained: “Figures showing higher percentages of candidates achieving good grades in one qualification than in another qualification would not necessarily mean the first exam was ‘easier’, but in this case that the candidates performed better.
“Similarly, the ‘chance’ of a candidate obtaining a given grade would not depend on the percentage pass rate for that grade, but on the quality of their work in the examination.”
GCSEs are regulated by Ofqual, which uses a statistical method called “comparable outcomes” to ensure that roughly the same proportion of pupils will be awarded each grade as in previous years.
Meanwhile, IGCSEs are not regulated by Ofqual, meaning that the number of top grades handed out are not in any way restricted.
An Ofqual spokesperson said: “GCSEs and International GCSEs are not the same qualifications, and so we have said it is not possible to say with any precision how the standards of the two compare.”