A three-year British police inquiry into the Paris car crash that killed Princess Diana has concluded that her death was a "tragic accident" and not the result of a high-level murder conspiracy.

"Our conclusion is that on the evidence available now there was no conspiracy to murder any occupants of that car, this was a tragic accident," said the former head of London police, John Stevens, who headed the investigation.

"I have personally ensured that every reasonable line of inquiry has been undertaken... we are confident that the allegations made are unfounded," said Stevens.

"I see nothing that would justify further inquiries with any member of the Royal Family."

The investigation into the Aug. 31, 1997, crash that killed Diana, 36, and her companion Dodi Al Fayed, 42, has been surrounded by rumours of conspiracies.

The couple was killed along with chauffeur Henri Paul when their Mercedes crashed in the Pont d'Alma tunnel while their vehicle was being chased by paparazzi.

The report concludes that Paul was drunk, twice the British legal limit, at the time and that the couple's travel plans had been changed by the pursuing paparazzi.

"We can say with certainty that the car hit the curb just before the 13th pillar of the central reservation in the Alma underpass, at a speed of 61 to 63 miles per hour (98 to 101 kilometres an hour),'' said Stevens.

"Nothing in the very rapid sequence of events we have reconstructed supports the allegation of conspiracy to murder.''

Stevens also said U.S. officials had assured him that secretly recorded conversations they had attained about Diana contained no new evidence into the circumstances of her death.

The U.S. National Security Agency said Tuesday while they'd never targeted Diana's communications they did have 39 classified documents containing references to the princess.

Claims of Conspiracy

Al Fayed's father, Mohammed, rejected the findings on Thursday, claiming their deaths were the result of a plot organized by British intelligence.

"The truth is being covered up," said a spokesperson for Al Fayed.

"I am the father who lost his son. I am the one who knows everything," Al Fayed, the Harrods department storeowner, said in an interview with BBC radio earlier Thursday.

As part of his theory, Mohamed claims that Diana was engaged to Al Fayed and that the Royal Family was furious that she was going to marry a man of Arab descent.

He also claims Diana may have been pregnant with his son's child.

But Stevens said their investigation showed that Diana was not pregnant and that she had no plans to get engaged to Al Fayed.

"Prince William has confirmed to me that his mother had not given him the slightest indication of such plans for the future," said Stevens.

A statement Thursday from the office of Prince Charles said Princes William and Harry had received a copy of the report and were grateful.

"They are extremely grateful to Lord Stevens and his team for the thoroughness and professionalism they have shown during their investigation, and trust that these conclusive findings will end the speculation surrounding the death of their mother Diana, Princess of Wales,'' the statement said.

Diana's brother, Earl Spencer, and her sisters Lady Sarah McCorquodale and Lady Jane Fellowes, also supported the findings.

"We have been briefed on the conclusions of the inquiry and agree with them entirely, and look forward to reading the full report in detail,'' their statement said.

Ongoing doubt

Despite a French judge's 1999 ruling that deemed the crash an accident, rumours and conspiracy theories have never been quelled.

The two-year French inquiry also blamed the crash on Paul, saying he was drunk, driving too fast and under the influence of anti-depressants.

A recent BBC poll found that 31 per cent of the sample still believed that the deaths were not an accident, while 43 per cent thought they were.

"No matter what the report concludes there will still be (conspiracy) points brought up," CTV's London Bureau Chief Tom Kennedy said Thursday.

"For example we do know that as they were driving into that Paris tunnel that night... the car they were driving hit another car... that car was never found and the eyewitness driving that car was never found."

"The security cameras in Paris that night, many of them were not working, so there's not a detailed security camera record of the movements of the car that night... conspiracy theorists will always say that this was something that was organized by very powerful people.

The inquiry, which involved 15 police personnel, is believed to have cost millions as investigators used computer technology to reconstruct the crash scene in 3-D.

Stevens also examined hundreds of witness statements, visited the crash site in Paris and held an interview with Diana's former husband, Prince Charles.

"I very much hope that all the work we have done and the publication of this report will help to bring some closure to all who continue to mourn the deaths of Diana, Princess of Wales, Dodi Al Fayed and Henri Paul," said Stevens.

The publication of the report will now allow an inquest into Diana's death to finally commence.

The inquest, which convened and then swiftly adjourned in 2004, will formally resume next year and will be headed by retired senior judge, Dame Elizabeth Butler-Sloss.

Preliminary hearings are scheduled to begin Jan. 8 at the Royal Courts of Justice.

With files from The Associated Press