In essence, this conspiracy theory holds that the British establishment murdered Diana in order to restore order and prevent a seismic shock to the ruling classes, either by revealing further secrets about her life with the royal family or by creating a constitutional crisis.
In 1998, Mohamed Al Fayed set the scene when he told the Daily Mirror:
"I believe in my heart 99.9% that it was not an accident. That car didn't accidentally crash. There was a conspiracy. I will not rest until I have established exactly what happened."
He alleged that Diana had agreed to marry his son and that because he was a muslim, forces in the British establishment conspired to prevent this ever happening by staging a murder that would look like an accident. Had Diana married Dodi, the step father of the future king would be a muslim.
15 years later, his idea of a conspiracy still looms large in some people's minds.
James Andanson was a part time paparazzo who is alleged to have been used by MI6 for various assignments. In the week prior to Diana's death he spent much time with her and her then-love Dodi Al Fayed aboard Al Fayed's yacht. It is said that he was taking photographs of the couple for exclusive publication. The following video offers perhaps the best overview of this idea.
After Diana's death, one fact remained unexplained by both the French and British investigations: paint left on Diana's car was identified as coming from a white Fiat Uno - but this Fiat was not found during the initial investigation (despite Mohamed Al Fayed offering a £1,000,000 reward and the search being the largest car search in French history). It is suspected that this car crashed into or clipped the Mercedes, possibly causing the fatal crash - although experts at the inquest stated that the collision would have been too minimal to effect events.
James Andanson was known to have owned a white Fiat Uno and repainted and sold the car three months after the accident, but forensic tests ruled out the notion that Andanson's car was involved. It had a quarter of a million miles on the clock and had apparently been on blocks for a considerable time when it was located.
In 2000, Andanson took his own life. His body was found horrifically burned inside his locked car. While some early reports quoted firemen as saying that he had gunshot wounds to his head, the inquest found that the holes had been caused by the intense heat of the fire that consumed the car. Weirdly, his car keys were never found - either inside the car or outside. How, ask the conspiracy theorists, could it be that a man so closely linked to Diana suffer such a mysterious death himself?
Of course, like all conspiracy theories, once examined the story quickly leads down a rabbit hole of denial and counter denial, claim and counter claim. Chief among the proponents of Andanson's involvement was Mohamed Al Fayed - Dodi's grieving father - who devoted much energy in the years following the crash to proving the complicity of British secret services in the death of his son.
Today, Al Fayed's website contains to hint at his continuing belief:
"I've always believed that Prince Philip and the Queen hold valuable evidence that only they know. They were not even questioned, but they should have been. No one should be above the law... The MI6 witnesses told us very little. I still believe they really know what really happened."
See also: conspiracy theories