The Diana files

No matter how wild the conspiracy theory, the British investigation into the death of the Princess of Wales is duty-bound to take it seriously. Martin Hodgson reports

The British inquiry into the death of Diana, Princess of Wales, is re-examining blood samples taken from the body of the chauffeur who was driving the car at the time of the fatal accident.

Forensic scientists working for Lord Stevens - the former Metropolitan police commissioner who is leading the inquiry - are studying samples taken from the body of Henri Paul in an attempt to explain unusually high levels of carbon monoxide found in his blood.

The disclosure came after a week of fresh allegations surrounding the inquiry - the latest in a series of claims, counter-claims and conspiracy theories that have swirled around the crash for nearly a decade.

Tests carried out during the official French investigation found alcohol levels in Paul's blood, which suggested that he was drunk at the time of the accident. They revealed that his blood contained more than 20 per cent carbon monoxide (CO), a level consistent with smoke inhalation or suicide.

A member of the legal team representing Mohamed al-Fayed, whose son Dodi also died in the crash, confirmed yesterday that investigators for the Stevens team are now re-examining the samples.

The French inquiry concluded that the high CO levels could have been caused by the car's airbag going off. But Mr Fayed's team says that airbags do not usually contain CO, and that Paul was killed on impact, so would have been unable to inhale the gas.

British investigators are examining three possible scenarios, the source said. "First, that there is a rational explanation for how such high levels of carbon monoxide got into his blood; second, that the results were mistaken - which casts doubt on the other results of the blood tests; or third, that it might not be his blood," said a member of the legal team.

Mr Fayed has long maintained that Paul's blood samples were substituted with those of another body to cover up a British intelligence operation to murder Diana, who he believes was pregnant with Dodi's child.

The exhaustive French investigation concluded in 1999 that there was no evidence of a criminal conspiracy, but it failed to scotch persistent rumours of foul play. Those rumours have been the staple of tabloid newspapers eager to keep the Princess in their headlines long after her death.

The most recent round of claims include allegations that two MI6 operatives were involved in Diana's "murder", and that the Queen's most senior courtier told a wireless operator at the embassy to leave his post half an hour before the car crash. A third allegation is that "British authorities" ordered the embalming of Diana's body before it was returned to England.

Possibly the most incredible claim was that the RAF crew that flew Tony Blair from his Sedgefield constituency to meet Diana's body in London had been on standby for two days before her death. If the allegation proves true, reported the Daily Mail at the time, "it would mean that Diana's death was not only expected - it was planned".

Lord Stevens has made it clear that his team is taking every allegation seriously. Last week, he said the inquiry had already proved "much more complex" and time-consuming than envisaged. "We had to investigate every conspiracy theory and rumour to prove or disprove them. We're not just looking at an incident in a tunnel in Paris. We're looking at that, and beyond all that," he said.

While the exhaustive nature of Lord Stevens's inquiries may suggest that he is taking the conspiracy theories seriously, observers of the case say that he is obliged to take every line of inquiry at face value - if only to avoid accusations that he has already formed his conclusions.

Yesterday, Mr Fayed said he was optimistic that Lord Stevens would present the definitive report into the crash, but he also warned that he would continue to press his own version of events. "[Lord Stevens] is a guy with great dignity and humanity. He will not be pressured from finding the truth. But if it ends up with a report which is a whitewash, of course I will not give up. This is my son I have lost," he said.

Mr Fayed's efforts have only added to the confusion surrounding the case, according to Martyn Gregory, the author of Diana: The Last Days. "The inquiry is a good deal more complex than envisaged because there are so many conspiracy theories, not because the case is complex," he said. According to Mr Gregory, the levels of CO in Paul's blood were consistent with those found in any heavy smoker.

"There was nothing unusual to the CO levels. By selectively quoting the results of the French investigation, the Fayed camp is trying to imply that something was amiss," he said.

Few observers believe that Lord Stevens's conclusions will differ significantly from those of the French investigation. Jennie Bond, the former BBC royal correspondent, said: "There is a small hard core of Diana fans who will never believe that she was the helpless victim of a drunk driver. But perhaps we should heed what her sons said: we should let her rest in peace."

Such hopes may be in vain. Lord Stevens admitted that the results of his inquiry will be front-page news around the world.

"The press see the deaths of Princess Diana and Dodi Fayed in the same light as the deaths of JFK and Marilyn Monroe," he said.

"People are watching and waiting to see what conclusions we come up with, so the thoroughness of the investigation is very, very important. We must do it absolutely right."

Conspiracy theories

The MI6 men

The claim: Two diplomats at the British embassy in Paris were MI6 operativesinvolved in a plot to "murder" the Princess.

The theory: She was killed to spare the Royal Family the embarrassment of the ex-wife of the heir marrying a Muslim.

The question: Why would they bother to kill Diana, when she had already told friends that the relationship with Dodi was not likely to last?

What the inquiry has found: Both men told detectives that they were out of Paris at the time of the crash.

The royal adviser

The claim: Sir Robert Fellowes - then the Queen's private secretary - ordered a wireless operator to leave his post in the British embassy in Paris half an hour before the car crash.

The theory: Mohamed al-Fayed alleges that the conspiracy to kill Diana was carried out on the orders of the Royal Family.

The question: Why would it take the Queen's most senior courtier to make sure the communications room was empty?

What the inquiry has found: Sir Robert - now Lord Fellowes - denied that he was in Paris.

The body

The claim: French legal official Maud Morel-Coujard - who supervised the police operation on the night of the crash - has said that "British authorities" ordered the embalming of Diana's body before it was returned to Britain.

The theory: It would foil any post-mortem pregnancy test.

The question: Why did the 1999 French investigation conclude that there was no evidence of embalming?

What the inquiry has found: Friends of Diana have denied she was pregnant.

The RAF plane

The claim: The RAF crew that flew Tony Blair from his Sedgefield constituency to meet Diana's body at Northolt had been on standby for two days.

The theory: As the Government was also involved in the plot, Mr Blair already knew that he would have to fly south.

The question: If the Prime Minister knew about the murder plot, why didn't he know what day he would need his plane?

What the inquiry has found: Detectives interviewed the security official, but have not said if testimony is credible.