THE integrity of the British exam system was at stake last night as evidence emerged of suspected grade manipulation with AS-levels - putting thousands more results in doubt.

As the head of the inquiry into the grades fiasco, Mike Tomlinson, delivered his initial report, Ampleforth College, near York, said it had evidence that English and history course work grades at AS-level had been deliberately depressed.

It came as Sir William Stubbs resigned as chairman of the exams watchdog QCA after Education Secretary Estelle Morris said there had been a breakdown of trust between the QCA and the examining bodies.

Mr Tomlinson, former Chief Inspector of Schools, said yesterday that students who did unexpectedly bad in their A-levels would have their papers regraded.

He confirmed that some papers had been inaccurately graded and that the actions of the exam boards had arisen from a perceived pressure from the QCA.

He said there had been no political interference in the exam process by Ms Morris, who had earlier faced calls to resign over her role in the investigation.

But The Northern Echo has uncovered growing concern that the crisis extends beyond A-levels.

Some schools now believe AS-levels - sat by lower-sixth form pupils - may also have been manipulated. But the report did not go into detail about AS-levels.

Father Leo Chamberlain, headteacher of the private Ampleforth College, said: "We have had serious problems with the grading of English course work at AS-level. We believe that the course work in some cases has been artificially depressed. In fact, as in other modules, it appears to have been by the use of a crude mathematical formula."

The course work papers were graded internally and then sent to a moderator who agreed with the teachers' marks.

But when the sample scripts came back from the exam board OCR, students found that, in some cases, their course work had dropped two grades.

If the crisis extends to AS-level papers then thousands more children will be drawn into the row.

Dr David Hempsall, treasurer of the Headmasters and Headmistresses' Conference, and headteacher at Queen Elizabeth Grammar School, Blackburn, Lancashire, said: "Tomlinson in his initial report makes no reference to AS-levels at all, and we shall want to raise that at the next stage of his investigation."

Liberal Democrat education spokesman Phil Willis said there needed to be a royal commission to look at the entire examination system from ages 14 to 19.

The Harrogate MP said: "There are questions being raised about AS-level and about GCSEs, so where does all this stop? The whole thing is just an absolute mess. Estelle Morris has got off scot-free when she was the person who, as Schools Standards Minister, designed the system."

Mr Tomlinson said yesterday that students would have to wait until Tuesday for his decision on which subjects and units should be regraded. But he said no one would be downgraded.

Huw Miller, 18, a former student of Yarm School, near Stockton, who was told to expect an A/B in his psychology course work but was awarded an unclassified, said the whole system needed to be looked at.

Huw, who got into his first choice of Northumbria University, at Newcastle, said: "I think we are very over-examined and it shouldn't be anything to do with politics."

David Dunn, head of independent Yarm School, said the Tomlinson report was "a vindication of the students and their hard work, and for the teachers who did their job properly".

Schools Standards Minister David Miliband, MP for South Shields, said that any changes to the exam system would only be made after consulting universities and schools.

Following his resignation, Sir William Stubbs said: "I was pleased that the inquiry exonerated me and found that I have operated properly. However, in the circumstances, to avoid any risk to the reputation of the QCA and its staff, I have offered my resignation as chairman."

A spokesman for exam board Edexel said: "The report confirms that all our grades were set within the ranges agreed by the chairs of examiners.