John Kerr accepts that the school examination system is "under stress" but he insists his organisation is coping.

He told me that, with 500 exam papers taken and a further 500 to go, he was "very pleased" with the progress Edexcel had made in improving its system for spotting, and correcting, errors.

Mr Kerr acknowledged the checks in the examination system could be changed radically but that the cost would be 'enormous'

He says the introduction of a new proof-reading check in January has worked well and, so far, no mistakes have got past it.

The proof-readers had spotted both of the errors that led to complaints this week.

In the first case, involving a misprint in a government and politics AS paper, the exam papers had been reprinted. Unfortunately, the printers sent out the old papers by mistake.

In the second incident, involving a business studies Vocational A-level, the proof-readers' vigilance meant an erratum slip was sent out to schools early in May.

Mystified

Edexcel says it cannot understand why the Anglo European School in Essex complained, as it received the erratum slip and even signed a registered post receipt for it.

John Kerr dismissed the calls from the NAHT leader, David Hart, for Edexcel's "licence" to be revoked.

He said he did not find Mr Hart's comments "helpful" as "all they have done was heighten the anxiety of students".

Turning to the wider problem, Mr Kerr said recent changes to examinations had put "very, very stretching demands" on the system.

He said the number of exam modules marked by Edexcel each year had mushroomed from just over four million in 1999 to an expected 10 million this year.

"Any business operation would struggle to cope with that increase in volume in such a short time", said Mr Kerr, "but we did it and we are floating".

Changes

Mr Kerr acknowledged the checks in the examination system could be changed radically but that the cost would be "enormous".

He said Edexcel had already invested �3m in a new telephone system, had taken on a new warehouse and created a new post-results service.

He also said late examination entries from schools were causing problems.

In January this year there were 27,000 late entries and 600 exam centres entered new candidates on the day of the exam.

He said Edexcel would still mark every late script but could not guarantee that the results for these entries would be out on time.

Looking ahead to further examination changes from the government's Green Paper, Mr Kerr warned that he would like to see "proper checks are made, piloted, evaluated and audited" to avoid any problems.