Conservative leader Iain Duncan Smith has joined calls for Education Secretary Estelle Morris to resign over A-level grade-fixing claims.

Ms Morris was accused by the chairman of the exams watchdog, Sir William Stubbs, of trying to prejudice an independent inquiry into claims that A-level grades for this summer had been fixed.

She [Estelle Morris] should either be sacked or resign

Iain Duncan Smith

The independent inquiry - led by former chief inspector of schools Mike Tomlinson - was ordered by Ms Morris last Thursday after schools claimed exam boards had deliberately marked down pupils' coursework to protect A-levels from claims they had become too easy.

Mr Tomlinson, who said he did not believe his inquiry had been compromised by the latest accusations, is due to publish his preliminary report on Friday.

The allegations by Sir William that Ms Morris instructed her officials to contact exam boards to discuss the possible re-grading of all papers in England - ahead of the publication of the Tomlinson report - have caused some to question her integrity.

Mr Duncan Smith said: "Her position is quite untenable. She should either be sacked or resign."

"Fiddling around with the inquiry, the A-levels scandal, which has wrecked so many children's lives - there's been endless chaos. It's time for her to go," he said.

Should she stay or should she go?

"She can't run her department if she is at war with the people that implement her policies."

Blair's support

Number 10 Downing Street was understood to be standing by Ms Morris.

Officials there reiterated Ms Morris's words that it was "perfectly proper" for the secretary of state to make contingency plans.

But despite backing from the Prime Minister, Ms Morris is still the person who will have to carry responsibility for the A-level row.

And the latest allegations have done nothing to restore public confidence in the exams system.

'Not up to the job'

BBC News Online's political correspondent, Nick Assinder, said Ms Morris was in serious trouble which could yet spiral.

He said there was a general feeling among Labour backbenchers that she had not been a good education secretary and was "not up to the job".

While many Labour MPs accepted that she was bright and able, there was a general view that she had been promoted too soon and was out of her depth.

Nick Assinder said, in terms of her future, much would depend on Mr Tomlinson's conclusions.

If his inquiry did uncover any interference by Ms Morris in the A-level grading row, she would have to leave her post - especially having denied any involvement.

"She's not under the cosh yet, but it is serious and it could come to that," he said.