Tory education reforms are giving private school pupils a huge additional advantage in the hunt for university places and jobs by allowing them to sit easier GCSEs than the more rigorous exams that are being forced upon state schools, new official figures suggest.

Data released in parliamentary answers, and research into the exams chosen by private schools, shows the extent to which the independent sector is still opting for less demanding, internationally-recognised GCSEs (IGCSEs), which state schools are progressively being barred from using.

Last night the Labour MP Lucy Powell, a former shadow education secretary, who received the data after tabling a parliamentary question, said it was now clear that reforms of the GCSE system had put state school pupils at a disadvantage compared with their private school counterparts.

“State school pupils have been treated like guinea pigs while many independent schools have gamed the system, insulating their institutions and their pupils against these changes, keeping the easier international GCSEs completely, or waiting for the new GCSEs to bed in before opting to enter their pupils on to these courses,” she said.

The parliamentary answers reveal that in 2017-18, 91% of international GCSE entries in core (EBacc) subjects such as English, maths and the sciences were in independent schools. A pupil in an independent school was 136 times more likely to sit an IGCSE than his or her counterpart in a state-funded school. Analysis of entries in all subjects shows that three out of every four IGCSEs taken were sat in private schools.

The Department for Education says that in the year in which a reformed GCSE subject is first examined, the equivalent IGCSE subject will be removed from Key Stage 4 performance tables, effectively meaning that state schools cannot use them.

A DoE spokesperson admitted that the new exams were tougher than the ones being widely used in private schools. “International GCSEs have not been through the same regulatory approval and quality control as the new gold-standard GCSEs, which is why we no longer recognise international GCSEs in school performance tables. The new GCSE qualifications have been reformed to provide more rigorous content, so young people are taught the knowledge and skills they need for future study and employment.”

Geoff Barton, general secretary of the Association of School and College Leaders, said private schools were within their rights to choose the internationally recognised exams, which include coursework, and should not be blamed – but added that the system was incoherent.

“This issue highlights the mess the government has made of the qualification system. It’s only a few years ago that Michael Gove was encouraging headteachers to introduce IGCSEs into their schools because it was seen as a better qualification than the GCSE,” he said.

“This was followed by hasty rewriting of GCSEs, stripping coursework out of most of them, and placing huge amounts of emphasis on final examination papers. Now the government has removed most IGCSEs from school performance tables, which effectively means state school pupils can no longer take these qualifications.

“Year 11 pupils typically sit more than 30 hours of examinations in the new GCSE system, and we are very concerned about the impact on their mental health and wellbeing.”

Analysis by Powell’s office of GCSEs on offer at top independent schools shows that none of the highest-performing schools puts their pupils in for the full suite of the tough new GCSEs in EBacc subjects. These core areas, which the government thinks it is important for young people to study to GCSE level, include English language and literature, maths, the sciences, geography or history and a language.

Pupils at £40,668-per year Eton College were only entered into IGCSEs in EBacc subjects.

Pupils at schools including the £37,296-per year boarding school Sevenoaks School and £17,040-per year Abbey School in Reading were only entered for IGCSEs.