Head teachers have called for the independent inquiry into A-level grading to be extended to cover "significant discrepancies" in the marking of GCSE exams.

The National Association of Head Teachers said it had evidence that GCSE entries in music, English literature and English language had been affected by "slipshod marking".

David Hart will ask Mike Tomlinson to widen his inquiry

David Hart, NAHT general secretary, said his members felt poor standards of examining, rather than malpractice, was to blame for these "very strange results".

"We are gathering evidence that it's not just A-levels, it's GCSEs," said Mr Hart.

"We've certainly had complaints of some very strange marking, both in GCSE music and in English literature and language."

Mr Hart said he was not yet able to say which exam boards were being held responsible for the rogue English results noted by NAHT members.

'Over-loaded' system

Mr Hart said he would be urging Mike Tomlinson, who is heading the independent inquiry into A-level grades, to look at GCSEs as well.

The former chief inspector of schools in England has been asked to examine claims that the exams watchdog, the Qualifications and Curriculum Authority (QCA), pressurised exam boards into lowering results to counter claims that A-levels had been dumbed down.

Mr Hart said: "What the NAHT will certainly be saying to Mike Tomlinson is that the examining boards are trying to run the most over-loaded, highly pressurised examination system in the world."

"The sheer volume of marking is inevitably leading in our judgment to slipshod, inadequate and rushed marking and that is why there is a rising volume of complaints coming from our members."

But a spokeswoman from the exam board, Edexcel, accused the NAHT of scaremongering.

The spokeswoman said the board was already dealing with calls from "distraught pupils and parents" worried about their A-level grades.

She called on the NAHT to produce evidence to back its claims and said complaints about GCSE marks were being dealt with in the standard way.