Exam boards chiefs in England and Wales have urged the Government to delay the introduction of diploma qualifications in academic subjects for secondary school pupils.

The Joint Council for Qualifications warned that the planned introduction of the academic diplomas alongside GCSEs and A-levels in 2011 could compromise quality.

The council’s letter, a copy of which has been obtained by The Sunday Telegraph, urged ministers “in the strongest possible terms” to delay the implementation of the academic diplomas.

Signed by heads of all the exam boards in England and Wales, the letter said: “The original timescale could only be achieved if we now compromise the quality of development in the areas of assessment and standards.

“Under the circumstances, rather than risk the quality of these important qualifications by compressing the development into a shorter remaining period, we urge you in the strongest terms to defer implementation for a year to allow for an integrated development of content, assessment and pedagogy.”

Diplomas in 14 vocational subjects began to be phased in last September, but the extension of the programme into three academic areas – science, humanities and languages – has caused controversy because of the overlap with GCSE and A-level courses.

Take-up for the first diplomas was around 12,000, about a quarter of the expected figure.

Jim Knight, the Schools Minister, announced last week that the advanced science diploma would be phased in over two years to ensure its quality, but he now says that there are no plans to delay the introduction of diplomas in languages and humanities.

David Laws, the Liberal Democrat schools spokesman, said that the letter showed the “shambolic” state of the diploma programme.

“The Government’s complicated fudge of running this huge new diploma programme against all the existing academic and vocational qualifications was always bound to end in tears and it is not surprising that young people do not wish to be guinea pigs for a system designed around political ends,” he said.

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