Officials representing Princess Diana have described as "unhelpful and upsetting" comments made by Mr Mohamed al-Fayed, who has claimed that the crash in which the princess and his son, Dodi Fayed, were killed was not an accident.
As the French investigation continues into the crash, speculation has mounted about Princess Diana's last moments and whether she could have been saved if she had been brought to a hospital sooner.
However, conspiracy theories similar to those espoused by Mr al-Fayed have angered the princess's family, Buckingham Palace and the French investigation team.
Responding to Mr al-Fayed's claims in the Mirror yesterday, a spokeswoman for the princess's office said: "We have no comment on the article, but this continued speculation is both unhelpful and upsetting to the family."
Buckingham Palace also moved to quash the speculation, saying it would be "inappropriate" to make any comment while the investigation was still under way.
In his interview, Mr al-Fayed said he had decided to speak out because of the "rubbish" that had been written about the cause of the car crash. He said he believed the crash was deliberate.
"I believe in my heart 99.9 per cent that it was not an accident. That car didn't accidentally crash. There was a conspiracy. I will not rest until I have established exactly what happened. I have great confidence in the investigators in Paris and I believe that we will find the truth."
Mr Fayed's driver, Mr Henri Paul, who was later found to have been over the drink-drive limit, was not to blame for the crash, Mr al-Fayed said. He said he had trusted him and he explained that drinking was an integral part of French culture.
"Everyone wants to blame the driver," he said. "It suits everyone to say it was just a drunken driver. I will find the person who caused this accident. I will not sleep. I will not rest until I have done so."
"I believe there were people who did not want Dodi and Diana to be together. If more had been done to treat Dodi and Diana, they could have been alive today," he added.
Mr al-Fayed also repeated claims made shortly after the princess's death that she had spoken to a nurse of her last wishes. He said the nurse had told him that Princess Diana wanted all her possessions in Dodi Fayed's Paris apartment to be given to the Duchess of York. He also claimed the princess wanted the duchess to "take care of my boys".
However, one of the doctors who treated Princess Diana after the crash questioned Mr al-Fayed's claim, saying she could not have spoken to anyone because of the extent of her injuries.
The hospital where the princess was treated has also denied Mr al-Fayed's account of her last hours.
Last night a spokesman for the Paris investigation team said they were not prepared to comment on Mr al-Fayed's claims. Mr al-Fayed has written to the judge investigating the crash in which the princess and his son were killed to examine a damaged white Fiat Uno that was sold in the Paris area last month. He believes another car may have been involved in the crash.
PA adds:Later, he disclosed how he had been shunned by Earl Spencer, the Prince of Wales and the Duke of Edinburgh since the deaths of Diana and his son.He told the Mirror that none of them had sent him messages of condolence since the car crash and that Princes William and Harry had been told not to speak to him."I gave the two princes one of the best holidays of their lives, but their father can't even be bothered to offer me condolences on the death of my son."I sponsored some of Prince Charles's polo tournaments and Prince Philip's Duke of Edinburgh Award schemes, but they want nothing to do with me any more."Does this show compassion and respect? I don't think so. It's disgraceful."