The threat was made despite promises by Ruth Kelly, the Education Secretary, that she will make mathematics and English GCSEs harder to pass.

Head teachers of independent schools are so concerned at how easy GCSEs can be to pass that many are considering entering their 14-year-old pupils for AS levels instead.

They have continued to use the present system in the knowledge that the Government has asked Sir Mike Tomlinson, the former head of Ofsted, to review secondary level qualifications.

David Vanstone, chairman of the Independent Schools Association, said that the Government’s refusal to reform the GCSE and A-level system and replace the exams with diplomas had left schools in limbo.

Nearly 600,000 teenagers are to receive their GCSE results on Thursday, with the number of pupils achieving good grades expected to increase once again.

Mr Vanstone, who is also head teacher of North Cestrian Grammar School in Altrincham, said that GCSE coursework was “stultifyingly boring” and open to cheating. He said: “The maths exam in particular is being made less challenging to make sure people get up to pass standards. One of the problems for the most able people is that they can get to the top grades sometimes as much as a year in advance.

“To move ahead at the pace they should go, people are going to need some further or more difficult tests.”

He added: “It would require a very bold move to send someone out into the world without these qualifications. But we are getting close to the point now where the bold steps will be made to try to move forward. Schools may get bold to the point of ditching GCSEs altogether in some subjects.”

Eton College has already announced plans to scrap GCSEs. Manchester Grammar School is switching to the internationally recognised IGCSE.

The independent sector supported Sir Mike’s plans to replace GCSEs and A levels with a diploma system combining academic and vocational courses. The Government rejected the plans. Ms Kelly insists that GCSEs will be retained, although English and mathematics are to be reformed.

Last night it was reported that an examination board used non-teaching staff to mark some GCSE papers. Edexcel drafted in administrative staff to meet the deadline for marking religious education papers, according to The Guardian. The company reportedly admitted that it recruited graduates to mark papers, after struggling to find religious studies practitioners.

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