Witness for the prosecution: 'Prince Philip is a Nazi... Tony Blair was in on it... So was Prince Charles... I believe my son and Princess Diana were murdered'

Mohamed Abdel Moneim Fayed cut a small, anguished figure as he strode slowly towards the witness box at the High Court yesterday. The grim smile spoke of the deep hurt of a grieving father, but there was also an unmistakable sense of triumph. Earlier, outside the court, he had declared "This is my moment" – and in a way it was.

As the Harrods owner came face-to-face with Lord Justice Scott Baker at the inquest into the deaths of his son Dodi and Diana, Princess of Wales, it marked the climax of his efforts to convince the world and a jury of the truth of allegations which add up to the most elaborate conspiracy theory ever presented to a British court.

Mr Fayed, 75, has spent 10 years engaged in the single-minded pursuit of what he believes is justice for his son and the woman he insists was about to become his daughter-in-law and mother to his grandchild. Before a packed public audience, he swore by Allah to tell the "truth, the whole truth and nothing but the truth". What then unfolded at the Royal Courts of Justice was by turns confrontational, at times bemusing, occasionally laugh-out-loud funny but at its core, deeply, deeply sad.

At the crux of Mr Fayed's version of what happened in the Pont d'Alma tunnel in Paris on the night of 31 August 1997 is a conspiracy of quite breathtaking dimensions. It was not a murder but a "slaughter", he raged. The couple were the victims of "terrorists ... gangsters" who just happened to include some of the most towering figures of the British establishment, he said.

Under cross-examination, the Egyptian-born tycoon spelled out exactly how he believed Diana was murdered and how he had been thwarted at every stage of his career by secret "stooges" in the judiciary, the Government and the media, many of whom had been ennobled for their services against him. The murder was, he said, the result of an audacious plot hatched by Prince Philip, who was not only a member of the Frankenstein family but also the real ruler of Britain and a crypto-Nazi. Philip was assisted by his son Prince Charles, Mr Al Fayed claimed; they were the two principal royal plotters, the senior male members of what he called a "Dracula family".

The accident was staged, he alleged, with the full knowledge of Prime Minister Tony Blair, his chief-of-staff Jonathan Powell and, most likely, the Foreign Secretary Robin Cook. He claimed the plot was similar to one hatched by the security services to dispatch the former Serbian President Slobodan Milosevic. The plan, Mr Fayed said, was masterminded from a secret communications centre in Paris, linked to the government listening station GCHQ by the Queen's Private Secretary, Lord Fellowes, who also happened to be Diana's brother-in-law.

Execution of the plot, he said, involved a paparazzi photographer James Andanson (who was, according to Mr Al Fayed, later murdered) and Diana and Dodi's chauffeur that night, Henri Paul. Both were part of an intricately coordinated joint operation between M16 and the French security services, with communications support from the CIA.

The method of killing, Mr Fayed told the court, was a flash of light used to temporarily blind Mr Paul, who was in the pay of MI6. The weapon, he claimed, was Mr Andanson's white Fiat Uno – a vehicle described by the coroner as "clapped out" and by one QC as the "world's lightest and least powerful car".

According to Mr Fayed, the conspiracy stretched even wider. French agents in the ambulances deliberately delayed the Princess's arrival at hospital so that she was beyond treatment. Once there, her body was embalmed, possibly on the orders of Lord Jay, then British ambassador to Paris and now head of the Foreign Office, to hide any signs of her pregnancy. Doctors then swapped Henri Paul's blood with that from another corpse to convince the world the chauffeur was drunk when his Mercedes hit the tunnel wall while being pursued by photographers.

The cover-up was equally complex, Mr Fayed said, involving not only Hervé Stephan, the French judge who led the inquiry in Paris, but also the former Scotland Yard commissioners Lord Stevens and Lord Condon. Also complicit was Diana's sister Lady Sarah McCorquodale and the Princess's lawyer, the late Lord Mischcon. Between them, Mr Al Fayed claimed, they suppressed the one piece of evidence which would corroborate his entire story – a handwritten note, concealed in a wooden box bearing the late Princess's initials, which was kept in her apartment under the faithful guard of her former butler Paul Burrell.

To add extra drama to this extraordinary testimony, Mr Burrell was pictured on the front of yesterday's Sun newspaper, claiming that he failed to tell the whole truth in earlier evidence to the inquest. Naturally, Mr Fayed ostentatiously brandished a copy of the paper for jurors to see – an astonishing performance on one of the strangest days in legal history. At one point, Lord Justice Scott Baker observed: "There seem to be an awful lot of people involved in this conspiracy." But Mr Fayed ploughed on, and the allegations piled up.

Then the cross-examination began, with gentle yet probing questions from Ian Burnett, QC for the inquiry, who paid tribute to Mr Fayed as not just a "great and buccaneering businessman but the father of a son who died". The Harrods boss was allowed to read out a statement in which he poured scorn on Lords Condon and Stevens for their roles in the three-year investigation, and accused them of helping to suppress a letter in which Diana apparently revealed her fears for her life at the hands of her father-in-law and former husband.

"They have no conscience, no courage and have given into the dark forces who want the note to stay secret," Mr Fayed said. "[Diana] said she was going to be killed in a car crash and this is what happened to my son. She told me that if [she] was ever killed or anything happened to her I must make sure the contents of this box were made public." Mr Al Fayed insisted repeatedly that the case was "black and white". Those who opposed his version of events were talking "baloney" or part of the conspiracy of "dark forces", he said.

Mr Fayed was asked to recall the fateful night when he was telephoned at home by one of his security staff and told that the couple were dead. Wiping away tears, he said Diana had suffered at the hands of the Royal Family for 20 years. "She could see happiness and love at the end in a family which she respected," he told the inquest. "They would not let her do that and they took my son with her."

Mr Fayed railed against his treatment at the hands of the British Establishment – not least over his failure to secure a British passport, an allegation that drew the then Home Secretary Jack Straw into the list of conspirators. Mr Fayed said he had "paid billions in taxes, employed hundreds of thousands of people, given millions to charity". "Is it fair that after that they murder my son?" he asked the court. He insisted he wanted to expose the conspiracy not for himself but "for the ordinary people". Turning to the jurors, he added: "I am sure they have children and they know what I am going through."

Mr Burnett responded by asking why it took Mr Fayed nearly six months to disclose in a newspaper interview the fact that the couple were set to marry – a claim his spokesman Michael Cole had already refuted several times. Mr Al Fayed said the matter was personal and Mr Cole had spoken "garbage".

Turning to Diana's alleged pregnancy, which he said had been dismissed in an "avalanche of evidence" to the inquest, Mr Burnett asked whether all the witnesses were liars. "Definitely," Mr Fayed hit back. He then claimed that Diana's friend Rosa Monckton was another agent of MI6 – and extended the accusation to her husband, the Independent columnist Dominic Lawson.

However, he reserved his most savage criticism for the royals. Of Prince Charles, he said: "I am sure he knows what is going on to happen because he would like to get on and marry his Camilla, and this is what happened. They cleared the decks. They finished [Diana], they murdered her and now he is happy. He married his crocodile wife and he is happy."

Mr Fayed described Prince Philip as the true power in Britain and the head of an "18th-century autocracy". "Philip is ruling the country behind the scenes," he said. "He is a racist as everybody knows, he will not accept us, as a person that grew up with the Nazis." He added: "You want to have his original name? It ends with Frankenstein."

Proceedings became more ill-tempered as Richard Horwell QC, the counsel for the Met Police Commissioner, began cross-examination. He disclosed that Mr Fayed had written to MP Paul Murphy in 2006, implicating Mr Blair and his "henchmen" in Diana and Dodi's "murder". As Mr Horwell probed deeper, the tycoon grew more irritated, at first refusing to answer and then, to howls of laughter from the public gallery, dismissing his questions as "silly" or "bullshit".

Asked why, if the killing was a plot to prevent a Muslim marrying into the Royal Family, that Diana was not murdered when she was dating the Pakistani surgeon Hasnat Khan, Mr Fayed replied: "How can she marry someone like that, who lives in a council flat and has no money."

It will be up to jurors to decide whether Mr Al Fayed's confidence in the wisdom of the "ordinary people" has been well-placed.

The accused

Prince Philip, Prince Charles, Tony Blair, Jonathan Powell, Robin Cook, Lord Fellowes, Lord Jay of Ewelme, Lord Stevens of Kirkwhelpington, Lord condon, James Andanson, Henri Paul, Herve Stephan, Lady Sarah McCorquodale, Lord Mishcon, Dominic Lawson, Rosa monckton, The Security Service MI5, Secret Intelligence Service MI6, The CIA, The French Secret Service, French ambulance service

Interesting? Click here to explore further