Ken Boston, chief executive of the Qualifications and Curriculum Authority (QCA), said: "If we succeed in delivering the 2003 summer examinations smoothly, it will be by good management rather than by luck, and by a hair's breadth."

Dr Boston said he was confident there would not be a re-run of last year's re-grading fiasco - in precisely the same way.

But he added: "That is not to say that there will not be an episode of another type in 2003.

"Conducting public examinations in the way we do is a high-risk activity in a very complex and fraught environment," Dr Boston told a public policy seminar in London.

Logistics

He said that thanks to changes introduced after the Tomlinson Inquiry into the 2002 results, the standards and the awarding process were now clear.

Teachers 'moonlight' as markers and are paid piece rates, and 24 million scripts move about the country at the whim of the Post Office QCA chief, Ken Boston

There were plenty of sample exam materials and communications had been improved.

But the operation was still logistically demanding.

"We have a 21st Century, internationally-celebrated qualification - the A-level - underpinned by an antiquated delivery system in which teachers 'moonlight' as markers and are paid piece rates, and 24 million scripts move about the country at the whim of the Post Office," he said.

External consultants had been hired to help with the project.

But he added: "I cannot assure you at the moment, with the degree of confidence I would like, that the smooth delivery of the examinations is assured."

Dumbing down debate

Dr Boston said that at the very least he expected "the annual August outcry about falling standards".

Only a minority of people understood the difference between maintaining the A-level standard and the number reaching that standard.

"So at the very least, high pass rates and substantial numbers of A grades will be taken by some commentators to mean that the currency has again been devalued."

As part of a confidence-building exercise, the views of teachers, students and parents were being sought.

Exam burden

A "students' roundtable" was being set up, to meet twice a year, whose views would be published.

He repeated his view that in the longer term the system was not sustainable.

"The system is at breaking point. It needs radical reform," he said.

Modernisation was one way forward.

But also, in his view, the assessment load for students could and should be reduced "across the full age range".