The IGCSEs are not an option for state schools

The Edexcel exam board said 7,500 in the UK sat the International GCSE (IGCSE) in maths this summer, compared with 2,500 the previous year.

For the first time, the number of entries from the UK exceeded those from abroad, which stood at 3,800 this year.

The exam-based IGCSEs were designed for overseas centres where coursework could not be externally moderated.

Now they are being taken up increasingly by schools in the independent sector, which tend to regard them as more stretching.

These schools are also reported to prefer the fact that coursework is optional and not compulsory.

State schools are not able to enter their pupils for IGCSEs as they only receive funding for approved exams - and these have not been accredited by the regulator, the Qualifications and Curriculum Authority.

The qualifications are not taken into account in the school league tables.

Centres 'doubled'

The Edexcel exam board also revealed 320 UK-based pupils sat an IGCSE in biology this summer, compared with 35 in 2005.

"Certainly the interest is there," a spokeswoman for Edexcel said.

"Some centres have expressed interest for next year, although we won't know until next March when entries are made."

The board also sets IGCSEs in English language and literature, geography, history, chemistry, physics, business studies and ICT.

They are also offered by the University of Cambridge International Examinations (CIE).

That board does not give details of entry numbers, but told the BBC the number of centres entering candidates for the exams had doubled in the past year from 100 to 200.

A spokeswoman said the international element of the exams was popular among private schools.

"Students can go on and study at universities across the world, it's very much an international qualification," she said.

'Let the market decide'

The Headmasters' and Headmistresses' Conference, which represents leading private schools, said state schools should be allowed to enter pupils for these exams as well.

"On what grounds should the government deny maintained schools this choice?" said HMC secretary Geoff Lucas.

"They are set by reputable exam boards, recognised by all universities and standards are comparable."

Mr Lucas said the IGCSEs had a "slightly different content" and a syllabus that gave teachers "more freedom to teach creatively".

"They also provide more opportunities for the high-flying, more able pupils to stretch themselves while providing a challenge for the more average students," he said.