The head of the QCA exams watchdog has called for the inquiry into alleged A-level grade fixing to be held in public.

Sir William Stubbs, chairman of the Qualifications and Curriculum Authority (QCA), made his call after head teachers said they had presented evidence that the QCA had leant on exam boards to lower students' grades.

I believe that this enquiry must be as thorough and open as possible in the time available

Sir William Stubbs, QCA

But the inquiry chairman - former chief schools inspector Mike Tomlinson - said he preferred to interview people behind closed doors.

This has prompted the Conservatives to ask what there is to hide.

The head teachers also said exam boards' staff confidentiality clauses had stymied their presentation.

What is there to hide if the witness himself wants to give evidence in public?

Damian Green, Conservative spokesman

But all the boards have now said they will let their most senior examiners speak freely to the inquiry.

Mr Tomlinson is due to present his interim report by Friday to the Education Secretary, Estelle Morris.

He is meeting the three main English exam boards on Tuesday.

'Massaged'

Among those he saw on Monday were the Girls' Schools Association and Headmasters' and Headmistresses' Conference - representing many independent schools - the National Association of Head Teachers and the Secondary Heads Association.

They showed him what they say are "bizarre" exam results - and complained that exam boards had been "leant on" by the exams watchdog, the Qualifications and Curriculum Authority (QCA).

"Our concern throughout this process has been to establish justice for this year's candidates at A and AS-level," they said afterwards.

They are not making public their evidence, so as not to prejudice the independence of the inquiry.

David Hart of the NAHT said it had produced evidence that chief examiners believed that coursework marks had been "massaged" downwards.

But he said the evidence remained anonymous because those examiners had a confidentiality clause built into their contracts.

Openness

The general secretary of the Secondary Heads Association, John Dunford, said it had been able to produce evidence from examiners only "in summary form" to protect their identities.

But on Monday afternoon the boards - Edexcel, AQA and OCR - all said they would be as open as possible with the inquiry and would not be holding their most senior examiners to the confidentiality clauses in their contracts.

The QCA is scheduled to meet Mr Tomlinson later in the week.

In a statement on Monday, its chairman, Sir William, said: "I believe that this enquiry must be as thorough and open as possible in the time available.

"Therefore, I have today asked that the enquiry be held in public, and if that is not possible, that evidence from QCA staff be taken in public and the QCA written evidence be made public."

Secrecy

A spokesman for Mr Tomlinson said his intention was that his inquiry should be as thorough as possible - albeit behind closed doors.

"If he thinks that seeing somebody would be of benefit, then he will call them - whatever it takes," he said.

"We are seeing people in private and the chairman feels that that is the way to proceed."

The Conservative education spokesman, Damian Green, said: "This is an alarming and disappointing decision.

"Pupils, parents and teachers deserve as open an enquiry as possible in the exam scandal and there is absolutely no reason why Sir William Stubbs should not give his evidence in public.

"It is vital that this investigation is not seen as a cover-up. Today's decision can only raise suspicion that the inquiry will not be completely open and independent.

"What is there to hide if the witness himself wants to give evidence in public?"

Mr Green has also called for an early debate on what he calls "this disgraceful mess"as soon as Parliament returns.

Head teachers have also called for Monday's deadline for requesting re-marks of exam papers to be extended, so those which believed their students had been treated unfairly could challenge their results.

Interference denied

Earlier the School Standards Minister, David Miliband, denied that he had used meetings this summer with the head of the QCA, Sir William Stubbs, to exert pressure to downgrade some results.

He said the issue had not been raised.

"I can give you an absolutely categoric assurance that at no stage did I interfere with the setting of grade boundaries in meetings with the QCA or with anyone else.

"At no stage was there any suggestion from me that there was a ministerial concern about the outcome of the grades.

"It would be quite wrong for politicians to be setting those sort of grade boundaries."

He said that the government was determined to find out what had happened to the grades this year through the Tomlinson inquiry.

"We are determined to get to the bottom of this to find out if anything was amiss," he said.

"If anything was amiss we have made it absolutely clear that we will act decisively," he said.