Martyn Gregory: Al-Fayed can't rewrite the death of Diana

If the inquest shows that justice cannot be influenced by a multimillion-pound PR campaign, taxpayers' money will be well spent

The media feasted last week on the dramatic and unexpectedly visual start to the Princess Diana and Dodi Fayed inquest, but many have asked why taxpayers should meet the estimated £10m bill for a six-month legal circus. Don't we already know that Diana was killed by a speeding drunk? I would argue, though, that the legally obligatory inquests are both valid and necessary. Lord Justice Scott Baker has stressed that the inquest will not apportion blame, but it will define history's verdict. Perhaps most importantly, it should demonstrate to future generations that justice cannot be influenced by those most closely involved or those with most to lose.

Had Diana never met the Fayeds, she would not have been killed in that awful car crash 10 years ago, unless the jury chooses to believe Mohamed al-Fayed's version of events, which, evidence-free, is that the Duke of Edinburgh organised Diana and Dodi's "assassination" at the hand of the late James Andanson, a French paparazzo. One problem with this theory is that Andanson was 160km from Paris when the crash happened.

The coroner told the jury that Mr Fayed's case was also that his own head of Ritz security, Henri Paul, was working as an MI6 "pawn". He had been "used by MI6 to get Diana and Dodi to a spot where the assassination plan could be put into action, namely the Alma tunnel".

One of Mr Fayed's three QCs at the inquest, Michael Mansfield, will illustrate to the coroner how this "assassination" was executed. It should be noted that lawyers cannot address the jury directly at an inquest – only the coroner can do this. Thus there can be no rhetorical flourishes as Mr Fayed's lawyers presumably try to prevent history's verdict falling on his family's name.

As the jury travels to Paris tomorrow with the coroner, members of Mr Fayed's gilded legal team will accompany them. They have to confront the fact that Diana was travelling from a Fayed hotel to a Fayed apartment in a Fayed car with a Fayed driver. The jury saw the last picture ever taken of the Princess sitting next to Mr Fayed's son and behind a Fayed bodyguard.

Before Diana was buried, Mr Fayed embarked on his multi-million-pound legal and PR effort to find someone, anyone, to take responsibility for the crash, other than his family or his current employees – some of whom were in situ when Diana died on the Fayed watch.

The Harrods press conference on 5 September 1997, the eve of Diana's funeral, provided the initial template for his campaign. In time it would target the French paparazzi; his own bodyguards (who both quit in 1998); his own head of Ritz security, Henri Paul; the 1997-99 French investigation that found that Diana died because Paul was drunk and speeding; the 2004-06 British investigation by Lord Stevens – Operation Paget – which looked into 175 Fayed "conspiracy claims" and found not one shred of evidence to support any of them; MI6 and the British embassy in Paris, and even the CIA.

The coroner is keeping "an open mind" as to whether to accede to Mr Fayed's insistence that Prince Philip and other members of the Royal Family be summoned to the inquest – a wise decision. If they do not turn up to respond to Mr Fayed's calumny, he will cry "establishment fix". If he fails to obtain an "open" verdict, he will take his ravings into cyberspace or, eventually, to the mausoleum he is preparing for himself at the top of Harrods.

Mute CCTV footage from the Ritz focused the jury's minds on the crucial hours before Dodi and Diana left the hotel. They provided some uncomfortable as well as some touching insights. Diana's mock salute to Henri Paul as the Mercedes drew up outside the Ritz appeared to indicate that she thought he was in control. She was tragically mistaken.

We also saw pictures of two limousines waiting at the front of the Ritz, and the professional chauffeurs, Philippe Dorneau and Jean-François Musa, who had brought the party to the hotel. Had they been allowed to perform their duty, there would be no need for an inquest. No qualified French chauffeur has ever been involved in a fatal crash.

Both bodyguards, Trevor Rees-Jones and Kez Wingfield, are seen in animated (inaudible) discussion with Dodi. Of the 20 issues laid out by the coroner for the inquest to consider, the central one is no 7: whose decision was it that the Princess of Wales and Dodi Fayed should leave from the rear entrance to the Ritz and that Henri Paul should drive the vehicle?

The bodyguards' objections to Henri Paul driving – he had never driven Mr Fayed anywhere in 10 years – were rendered pointless by Mohamed himself. They claim that, in a phone call with Dodi, the father approved the son's plan to leave his hotel. They also say they had to argue strongly with Dodi even to allow Mr Rees-Jones to travel in the Mercedes, while Mr Wingfield was dispatched to create a "diversion" with the two official chauffeurs. The CCTV pictures showed this fateful process taking place as Diana waited unsuspectingly to die.

In 1998 Mr Fayed accused the two bodyguards of being responsible for the crash and, later, of being "turned" by MI6. Their appearance before the inquest – scheduled for next month – will be crucial. Both men have successfully defended their positions in court. Both categorically deny any link with MI6 and neither retains links with Mr Fayed.

The CCTV pictures of Dodi's return to the Ritz from a brief visit to the jeweller, Repossi, were also fascinating. On Wednesday, the coroner quoted Mr Fayed's mouthpiece, Michael Cole. He had initially been uncertain as to the provenance of the ring that Mr Fayed today displays in Harrods as the couple's "engagement ring". On the eve of Diana's funeral, Mr Cole said: "Dodi gave [it] to the Princess only hours before their deaths. What that ring meant we shall probably never know."

Yet the ring has now, according to Mr Fayed, become a central element in the Royal Family's desire to wipe out the possibility of a Muslim stepfather for princes William and Harry.

The CCTV pictures have raised the question of whether Dodi himself actually bought a ring at all. They showed that he left Alberto Repossi's shop close to the Ritz on 30 August with only a catalogue. Later a Ritz official visits the shop and returns to the hotel with a package. This is believed to have contained a selection of rings for Dodi. The CCTV later shows the Repossi package being placed in the hotel safe.

No evidence was offered this week that Diana ever saw Mr Repossi's creation. Nothing has been produced to suggest that she had been proposed to by Dodi, or that she would have accepted such a proposal. Lord Stevens obtained CCTV footage of both the 30 August visits, which appear to challenge the jeweller's 2003 claim that he personally placed the ring on Diana's finger. Operation Paget found no evidence that Mr Repossi ever met Diana. His appearance at the inquest will thus be most interesting.

Martyn Gregory is the author of 'Diana: The Last Days' (Virgin Books, £6.99). He is commenting on the inquest for Sky News