The sister of Diana, Princess of Wales entrusted a "Pandora's box" of secrets to butler Paul Burrell in the aftermath of the fatal Paris car crash, an inquest was told.

Lady Sarah McCorquodale said its contents were given to Mr Burrell, Diana's aide, but the sensitive documents - including Diana's divorce papers - have never been seen since.

The large wooden box is at the centre of claims it contained "nasty" letters from the Duke of Edinburgh to Diana and other embarrassing material that Lady Sarah destroyed to stop it causing distress to members of the Royal Family in the future.

But Lady Sarah told the court she was "100%" confident there were no letters from the Duke in the box - despite a note from policeman Roger Milburn which suggested there had been.

Mohamed al Fayed is convinced Philip ordered Diana to be murdered by MI6 and believes her father-in-law's letters may hold the key to her death.

During her wide-ranging evidence, Diana's sister also said there was a "strong possibility" that the Princess' relationship with former lover heart surgeon Hasnat Khan could have ended in marriage but her later romance with Dodi did not "have much longer to go".

In the months following Diana's death the executors of her estate - mother Frances Shand Kydd and Lady Sarah - spent days shredding documents found in the Princess' Kensington Palace home.

Police, who searched Mr Burrell's house as part of an investigation into whether he had stolen some of Diana's property, found no trace of the contents of the box.

The inquest was also told by Lady Sarah that Diana believed Mohamed al Fayed was spying on her, during her final trip on his luxury yacht.

She also rubbished suggestions that Diana and Dodi had become engaged.