A British expert told an inquest into the death of Princess Diana on Thursday that he doubts that a sample of blood showing a high level of alcohol actually came from the driver of her car.

Mohamed Al Fayed, whose son Dodi died with Diana in the crash on Aug. 31, 1997, has alleged that the blood tests were faked to pin the blame on driver Henri Paul, who also died.

Al Fayed contends that the couple were the targets of a murder plot headed by Prince Philip, the husband of Queen Elizabeth, and carried out by British agents.

Professor Atholl Johnston, a clinical pharmacologist, said he was suspicious of the consistency of the results reported by French investigators and the high level of carboxyhemoglobin in Paul's blood, indicating an exposure to carbon monoxide.

French investigators reported that Paul was three times over the legal limit for driving in France. They reported alcohol concentration readings of 1.74 grams and 1.75 grams per liter from two samples of blood, and 1.73 grams per liter from a sample of vitreous humor from the eye.

Johnston, who was hired by Al Fayed to review the French tests, estimated the likelihood of getting such close agreement among three separate samples at one in 10,000.

"What are you suggesting — that that suggests to you that the results had been cooked?" coroner Lord Justice Scott Baker asked.

"That would be my interpretation," Johnston said.

Experts said that anyone with such high levels of carboxyhemoglobin would have a severe headache, but video images and witness accounts have not indicated that Paul showed any distress.

Johnston said it was unlikely that it was a measurement error.

"The most likely explanation is that it isn't Henri Paul's blood," he said.