Burrell vows to take Diana's secrets to the grave - despite agreeing to appear at her inquest

The former royal butler has told a family friend he is determined not to be "used" by Mohamed Al Fayed when he takes to the witness box at the High Court on Monday.

It is one of the most eagerly anticipated events of the sensational six-month hearing.

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Mr Burrell fears the Harrods tycoon's highly-paid team led by barrister Michael Mansfield - whose questioning of the late Princess's close friend Rosa Monckton drove her to tears - wants to use his appearance to lay bare the Royal Family's most intimate secrets.

In 21 years of service, he worked for the Queen as her personal footman before becoming Charles and Diana's butler at Highgrove.

Following the couple's separation in 1992, he moved to Kensington Palace with Diana where he became a trusted confidant.

While he was subsequently accused by her sons of a "cold and overt betrayal" in writing about his relationship with the late Princess, Mr Burrell has always insisted that he published only a fraction of what he knows.

His co-author of A Royal Duty, Steve Dennis, said last night that he agreed to attend the inquest because he firmly believed it was the only way to put an end to the damaging speculation that continues to surround her death.

"Paul is grateful for the opportunity to appear as a witness at an inquest he believes should have happened many years ago,' he said.

"Contrary to some media speculation in recent months, he is not attending to "dish the dirt" or reveal secrets.

"He is appearing in the interests of the truth and the memory of Diana, Princess of Wales, and to assist the coroner.

"Like everyone else, Paul is sensitive to the fact that two boys lost a mother and a father lost a son, and he appreciates that everyone shares a common goal in separating the truth from the myth and the fact from the fiction.

"I think his testimony, from the vantage point of his unrivalled position and trust alongside the princess, will be both significant and compelling."

Mr Burrell, who flew in from his home in Florida yesterday for the hearing, is due to spend an entire day giving evidence and being cross-examined.