Exam boards bowing to political pressure to make exams more “accessible” could be one reason for the grade inflation of recent decades, the head of research at a major board has admitted.

Tim Oates acknowledged that investigating the possibility could be a “Ratner moment” for exam boards, a reference to the jeweller who sent the value of his shops plunging by admitting that they sold “crap”.

But the head of research for Cambridge Assessment - parent company of the OCR board - said he wanted to start a debate about why the number of pupils getting the highest grades rises each year.

He said that increasing access in exams, updating content, switching to modular papers and being as transparent as possible over mark schemes, grade criteria and guidance, have all been “fervent preoccupations of policy-makers and the education establishment”.

“Awarding bodies delivered on that agenda,” Mr Oates said.

“Giving the benefit of the doubt to pupils - consistent with the general moral sense of ‘access’ and ‘best chance’ which was foremost in the political agenda - can result in subtle grade inflation,” he added.

“Constantly enhancing the ‘accessibility’ of questions, the transparency of mark schemes and the precision of guidance can ease up the numbers gaining the highest grades.”

His comments came in an article that was the opening salvo of an online discussion about exam standards being run by Cambridge Assessment, which will culminate in a live debate in London next month.

Mr Oates argued it would be “profoundly dysfunctional” for exam boards not to look critically at the techniques they use and that it is important for them not to follow orders “blindly”.

He said there is a strong case for saying that government-instructed changes such as the modularisation of A-levels in 2000 have been in excess of what was needed to keep exams up to date.

They have made maintaining standards over time more technically demanding and expensive. But not impossible, according to Mr Oates, who said assessment is “an exact science”.

Professor Roger Murphy, from Nottingham University, disagreed, saying exam grades are “approximations” that do not stand comparison over time or between subjects.

Both men will be taking part in the debate at the RSA in London on April 29. For a free ticket contact Lizzie Hale or Jennifer Roberts at expertview@cambridgeassessment.org.uk or telephone 01223 553462.

To take part in the discussion go to http:examstandardsdebate.org.uk.