The head of the exams watchdog who lost his job in the row over A-level grades says he is going to sue the government unless he gets a public apology.

Sir William Stubbs claims he was humiliated when he was sacked by the former Education Secretary Estelle Morris at the height of the row over alleged grade-fixing of A-levels.

As chief executive of the exams regulator, the QCA (Qualifications and Curriculum Authority), he had been accused of pressurising the exam boards to keep A-level grades at a similar level to last year.

He says his reputation has been ruined and he plans to sue the government for wrongful dismissal if he does not get a public apology and compensation.

Shocking

Sir William revealed exclusively to BBC News that on Friday, government lawyers would receive a letter from his lawyers, outlining his case.

He told BBC News: "What we will be saying is that my dismissal last month by the former Secretary of State for Education, Estelle Morris, was a shocking and saddening experience."

"It was carried out in a very public and humiliating way which caused great anguish to me and my family."

Sir William said he was sacked an hour before the release of the Tomlinson report into the A-levels crisis, which he said exonerated him.

The Tomlinson inquiry said the exam board executives had felt under pressure to deliver exam results which were in line with 2001.

Confidence in the exams system was damaged

But it also said that the QCA had acted properly, in line with its responsibilities as the exams regulator.

Sir William was not criticised in the report and says it vindicated him.

The report's author, Mike Tomlinson, said it was the sheer complexity of the AS-level and A-level system that had created an environment of confusion.

As a result of regrading, more than 1200 A-level students and 700 AS-level students had their grades improved.

'Not going quietly'

In previous interviews, Sir William said he had been told to jump before he was pushed.

He said Estelle Morris had said if he went quietly she would speak kindly about his work in education.

He wrote a letter of resignation.

Sir William says he is prepared to fight in the courts to restore his good name.

"I am not going quietly because I was maligned, because this is important to me. I'm determined to pursue this, if necessary through the courts," he said.

Estelle Morris insisted he had to go because he had lost the trust of the exam boards and schools and his departure would help to restore confidence.

The department for education denies that Sir William was ever threatened.

Earlier this week, the department received a personal letter from Sir William complaining about what happened to him.

On hearing of the lawyers' letters being sent, officials made this comment:"We received a letter from Sir William Stubbs earlier this week and today are sending an acknowledgement.

"We have not yet seen the second letter."