SIX subjects, including English, face problems finding people to mark exams as changes to the post-16 curriculum produce a bumper field of entries this summer.
The Joint Council for General Qualifications, the exam boards' collective body, this month sent a letter to schools and colleges appealing for more teachers to become examiners.
The joint council originally had to find around 8,000 more examiners this year. They have been hit by shortages for information and communication technology, general studies, media, art and psychology, as well as English.
Awarding body Edexcel is offering a pound;200 bounty for existing examiners who recruit other markers. Most exam boards still have lists of vacancies on their websites.
John Dunford, general secretary of the Secondary Heads' Association, said. "This has been a crisis waiting to happen. It's not just the fact that pupils are sitting more exams, but that teachers' workload is such that they are having to resign from acting as examiners."
Last year, examiners marked 771,809 A-levels and 5,481,920 GCSEs. This year the are expecting a 20 per cent increase.
The stresses on the system have led to fears that the chaos in Scotland last summer, when thousands of candidates received wrong or incomplete results, could happen south of the border this time.
The three English exam boards that deal with the majority of GCSE and A-level entries insist they are on-course to recruit enough new examiners and get results out on time.
A spokesman from the joint council said: "If we don't get the number we need we could redistribute scripts to the examiners we have. Examiners could also be switched between awarding bodies to cover shortfalls."
Some students face up to eight hours of exams in one day, and there is a record number of exam clashes. For instance, Edexcel has scheduled AS biology and economics at the same time as AQA is examining religious studies.Colchester Sixth Form College has about 100 clash candidates who will have to be supervised overnight.
The June 7 general election also clashes with GCSE English and geography and A-levelAS-level French, history and maths.