He told jurors Mr Al Fayed’s beliefs may be genuine but he added: “A belief expressed in legal proceedings which is unsupported by evidence is worthless.”

Diana, Dodi and their stand-in driver Henri Paul, the acting security manager at the Paris Ritz Hotel, died after their Mercedes hit a concrete pillar in the Alma underpass in Paris just after midnight on August 31, 1997.

There was laughter in court as the coroner made a reference to John Loughrey, a self-confessed Diana “superfan”, who has attended every day of the inquest.

He told the jury: “No one except you and I and, I think, the gentleman in the public gallery with Diana and Dodi painted on his forehead has sat through every word of evidence.

“No one is as well-equipped as you are to decide the facts of the case.”

Summing up the evidence, he dismissed claims by renegade former MI6 officer Richard Tomlinson that rogue MI6 agents may have murdered the couple, using a bright flashlight in a plan echoing one to assassinate Serbian leader Slobodan Milosovic in the early 1990s.

The coroner suggested Tomlinson was wrong and had fabricated his claims to embarrass his former MI6 bosses. No flashlight was mentioned in the first drafts of his book, which had described the assassination plot as a drive-by ambush.

The coroner said there was a welter of evidence to suggest Diana was on the pill, had a period mid-August and was anxious not to get pregnant.

“The only evidence that Diana was pregnant comes from the mouth of Mohamed Al Fayed,” he said, pointing out that the Harrods tycoon claimed the Princess told him she was expecting in a phone call an hour before her death.

“On the other hand, there is a great deal of evidence that she was not pregnant, although you may think it cannot be proved with absolute scientific certainty that she was not.” He added: “The issue fairly and squarely raises Mohamed Al Fayed’s credibility. Is he a man on whose word you can rely?”

The coroner suggested there was no evidence to support claims that Diana’s body was embalmed illegally to cover up her pregnancy. The embalming was done lawfully and Home Office pathologist Dr Robert Chapman, who carried out a post mortem on the Princess in London, said it would not have prevented him finding evidence of a foetus. He did not find anything, he said.

On claims that the couple were engaged and had bought a ring, he suggested there was conflicting evidence. He also said nothing had been found to support claims Prince Philip sent Diana threatening letters. He also dealt with the Princess’s fears, famously expressed in a note to her butler Paul Burrell and in a conversation with her lawyer Lord Mishcon, that she was in danger of  being killed on the orders of her royal in-laws.

He noted several of Diana’s confidants said she regularly expressed fears for her safety but they were never sure how seriously to take them. “You will have to decide whether Diana did truly fear for her life and, if she did, whether such fears were justified,” he said.

The coroner will continue summing up today. The jury is expected to retire to consider its verdict tomorrow.