Mr Fayed has written to the judge heading the investigation asking him to examine a damaged white Fiat Uno that was reportedly sold last month. Investigators believe the Mercedes that carried Diana and Dodi on the night they died may have struck the Fiat before slamming into a pillar in a Paris traffic tunnel.
Mr Fayed's claim that the crash was the result of a conspiracy has drawn an unprecedented statement from the Princess's office that her sons Princes William and Harry are upset by the continuing speculation. "We have no comment on the article, but this continued speculation is both unhelpful and upsetting to the family," said a spokeswoman for the Princess's office.
Diana's brother, Earl Spencer, said: "I have one question: 'Is there any good in all this speculation?' I ask that because there is clearly a lot of harm in it. All we, her family, ask is that Diana's memory be respected, and that sensational speculation be left out of the public arena, where it undermines all our aims to come to terms with our loss."
Investigators in Paris refused to be drawn by Mr Fayed's remarks, with one saying: "Mr al Fayed has his own opinions but we are not prepared to comment on them."
Mr Fayed's lawyer, Georges Kiejman, sent a letter to the investigating judge on Wednesday to let him know that a damaged white Fiat Uno was sold to a garage in the Paris region in January, a judicial source in Paris claimed. Mr Kiejman found the car through a private investigator.
A source close to the judge was yesterday reported as saying: "This prolonged period of grieving has certainly affected the way [Mr Fayed] is looking at hard facts. More than 100 detectives have failed to turn up any evidence of a conspiracy."
Mr Fayed's public allegation that the crash was not an accident will fuel the conspiracy theory mill.
At first, the theories were largely confined to the Arab media. For the most part, people were prepared to accept that the Princess's death was an accident which could have happened at any time. Yet as the investigation into the tragedy dragged slowly on, so the rumours have grown.
Within hours of Diana's death, newspapers received calls claiming the crash was not an accident. But the conspiracy theory really took hold three weeks later as it emerged that a white car, described as a Fiat Uno, had been involved in the accident but had mysteriously disappeared. Furthermore, the existence of the car had at first been denied by the French authorities.
Then on 22 September, Time magazine, published an article stating that a doctor claimed to have been informed by a colleague, who treated the princess at the crash scene, that she had told him that she was six weeks pregnant. People remembered that Diana told journalists last summer: "You will have a big surprise coming soon, the next thing I do." This followed the publication of photographs in which she appeared to have a slightly swollen stomach.
It was also recalled she told friends she believed her days were numbered because she was regarded as a "loose cannon".
Her relationship with the Muslim son of Mr Fayed, someone who did perhaps more than any other individual to undermine the reputation of the former Conservative government, could be seen as the ultimate insult to parts of the establishment.
In a new book, Death of a Princess: An Investigation by Thomas Sancton and Scott MacLeod , the authors speculate that Diana's alleged pregnancy was the most "explosive element" in the whole affair.
They write: "For the mother of the future King of England to bear the child of an Arab and a Muslim, a child who would be the half-sibling of the heir to the throne, would be embarrassing and problematic in the eyes of the Royal Family and the ruling Establishment."Reuse content