Britain's three largest examination boards are to ask the government for �6m to overcome a shortage of markers.

If Edexcel, AQA and OCR get the cash, it will be given to schools to take on more supply teachers, while permanent staff take time off from the classroom to mark papers.

The boards will have 24 million GCSE and A-level scripts to check this year.

AQA spokesman George Turnbull said: "Schools are finding it more difficult to release teachers for marking, with the amount of duties they have to fulfil.

Time pressures

"They have to be substituted with replacements and that costs money."

Education Secretary Charles Clarke promised an extra �6m to recruit more A-level markers last December.

The boards will be asked to bid for the money. They are to send a joint letter to all schools and colleges this week explaining the situation.

An investigation into allegations of grade fixing last year led to the upgrading of almost 2,000 students' A-level and AS-level results.

Tomlinson report led to upgrades

Following a review set up by the report's author, Mike Tomlinson, grades were raised in 10 A-level subjects and four AS-level, all with OCR.

Late changes to grade boundaries by the head of OCR, Ron McClone, were at the heart of the crisis.

But, despite the regrades, dissatisfaction has continued, with hundreds of students choosing to resit their A-levels this summer.

The division of the A-level into AS and A2 stages has also increased the marking workload, as students are graded in both the first and second years of the course.

Mr Turnbull said: "The shortage of markers is a national problem, not just that of one board.

High demand

"There are a lot of other pressures on teachers, such as those for the school to do well in league tables."

We are entering an Alice in Wonderland world when teachers are taken out of the classroom to mark exam scripts Damian Green, Conservative

Essay-based subjects, such as English, are especially demanding of examiners' time.

Last year, there was a particular shortage of markers in this subject and business studies.

Dr Ken Boston, chairman of the Qualifications and Curriculum Authority, which oversees the exams system, has said he cannot guarantee the smooth running of this year's A-levels.

A QCA spokesman said: "It is essential that any new initiative does not compromise the high standard of marking required. "

Tory education spokesman Damian Green said: "We are entering an Alice in Wonderland world when teachers are taken out of the classroom to mark exam scripts.

"The point of exams is to test the amount of learning that has taken place.

"When the exam system is reducing the amount of learning, it is doing more harm than good."

The solution was to reduce the number of exams by cutting the AS level.