Standards in GCSEs and A levels risk being dumbed down unless the new independent examinations watchdog is given statutory powers to force exam boards to maintain them, the Government has been warned.

In a highly unusual intervention into the debate about exam standards, Mike Cresswell, director-general of AQA, Britain's biggest exam board, has broken ranks with its rivals.

In an interview with The Times, he has given warning that public confidence in the quality of GCSE and A level qualifications cannot be maintained unless the new exams watchdog, Ofqual, has sufficient muscle to prevent exam boards lowering their standards.

Ofqual was created by Gordon Brown and made independent from government precisely to put an end to the debate about the dumbing down of public examinations and to ensure that there could be no suspicion of government pressure on exam boards to set standards at particular levels. But Dr Cresswell believes there is a “major omission” from the proposals for Ofqual's powers. While it is empowered to force exam boards to follow certain procedures in the way they set and mark exams, it has no powers over what level they set standards at.

“Ofqual needs to be given an explicit statutory power to enable it, if necessary, to direct an awarding body to set standards at a particular level,” Dr Cresswell said. “It needs to have this power so that it can give credible public assurance that standards are comparable between awarding bodies and maintained over time.” Without statutory powers of intervention, Ofqual would be left to the mercy of exam boards, he added. “A regulator who is there to uphold public confidence in standards can't be in a position where it has to negotiate with the exam boards over standards.”

Dr Cresswell added: “The awarding bodies compete for entries. They don't compete on standards. If Ofqual had this power [to enforce standards], it would make it much more difficult for that to ever begin.”

The main exam boards work closely together in developing qualifications, but there is a tension in their relationship, as they are competing with each other within a finite but lucrative market place. Schools and colleges pay about £400 million a year in fees to exam boards. Mr Cresswell's warning comes after a disagreement this summer between England's three exam boards, which set their own GCSE and A-level papers, about standards in the new GCSE single science exam. The three boards met in August to discuss grade boundaries. They failed to come to an agreement over the mark needed to get a C, officially a good pass. One of AQA's rival boards awarded Cs in one paper to pupils who got only 20 per cent of questions correct and would not back down from this position. Negotiations between the boards broke down.

AQA was eventually persuaded by Ofqual to reduce its own grade boundaries to bring it into line with the other boards, even though it did not think this sufficient to maintain standards. Dr Cresswell agreed to the move “under protest” because he did not want to disadvantage the half-million pupils who had taken his board's science exam. “Plainly, we couldn't possibly have a situation where children doing our exam would be judged against harsher standards than children doing other boards,” he said.

Yesterday was the last day for submissions on what monitoring and enforcement powers Ofqual should have. Dr Cresswell has written to the Government to express his concerns and to request a meeting with Jim Knight, the Schools Minister.

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