The past two years have seen a rush of commercial tie-ups, with examiners and publishers collaborating on approved textbooks promoted by the examination boards. But now the Government's exams quango, the Qualifications and Curriculum Authority, has warned them to tone down the sales pitch and abandon the "official" tag as complaints mount from schools, authors and rival publishers.
The QCA has told the exam boards in private that candidates without the endorsed publications could suffer.
The practice may also break competition law. James Sale, chairman of the Society of Authors' educational writers group, said: "There is a cartel being created here that undermines fair competition and restricts public access to the best books."
Deals causing concern include some struck by publishers Heinemann, which has produced "official" GCSE textbooks in maths and history for the London-based Edexcel exam group.
The QCA appears to have reached an agreement with the boards that schools will not be pressured into buying anything which claims to be the only approved text. New rules due out next March could even prevent authors from stating their position as examiners.
It is thought unlikely that the Government or any of its agencies could go so far as to ban chief examiners from writing textbooks altogether.
Edexcel has already asked Heinemann to remove the word "official" from its catalogue.
Fiona Clarke from Oxford University Press said that publishers have also agreed to stop using the word.
"People feel pressure to buy official books. Schools are saying to us, we'd like to use OUP textbooks but we have to use the official publications.
"In the past couple of years there have been a lot of deals done behind closed doors. In effect it's anti-competitive."
Sue Wharton, senior humanities publisher with Heinemann Educational, said:
"This sort of relationship is very new and people have been finding their feet. Whenever we've used a word like 'official', it's been
with the approval of the exam board."
A spokeswoman for the QCA said the agency will issue new rules on exam boards in 2000 and is still considering the issue.