On instructions from the highest level, Scotland Yard detectives are examining allegations that the British Army’s elite special forces regiment was involved in the Princess’s death in Paris nearly 16 years ago.
The claims came to light during the recent second court martial of Danny Nightingale, the former SAS sniper who was convicted of possessing an illegal firearm.
Ken Wharfe, the Princess’s former Metropolitan Police bodyguard, questioned why it had taken so long for the allegations to be aired.
He said: “The police have to look at it because of the level of the crime alleged. But if this was an allegation of a tinpot burglary a decade earlier, you would be lucky if a traffic warden would have looked at it.”
Former chief superintendent Dai Davies, the Met’s head of royal protection at the time the Princess died, said an inquest and two police inquiries had proved that her death was “an accident by any definition”.
“I’m mystified … how any new information can possibly allege anything other than [that]this was a tragic accident,” he added.
The murder claims were made in a seven-page handwritten letter written by the parents of the estranged wife of “Soldier N”, a former member of the SAS who was a key prosecution witness at Sgt Nightingale’s trial.
In September 2011 they wrote to the regiment’s commanding officer, raising concerns about their son-in-law’s allegedly erratic and threatening behaviour.
The letter, which was censored before being released to the court martial, states: “He [Soldier N] also told her [the daughter]that it was the XXX who arranged Princess Diana’s death and that has been covered up. So what chance do my daughter and I stand against his threats?