Princess Diana's chauffeur Henri Paul may have had eight alcoholic drinks the night he died, her inquest has heard.
Henri Paul's body was incorrectly labelled, it was heard
Bar staff at Paris's Ritz hotel said he drank two 50ml liqueurs that night.
But his blood alcohol level - 1.74g of alcohol per litre of blood - was twice the drink-drive limit for UK motorists, the court heard.
Pathologist Professor Robert Forrest, who also doubts the quality of the blood samples taken, said this was more consistent with eight drinks.
Princess Diana and her companion Dodi Al Fayed died with Mr Paul in a car crash in Paris in August 1997.
Professor Forrest told the jury the test results were "unlikely to reflect taking two 50ml doses of Ricard (liqueur) in the couple of hours or so before death".
"It is likely to reflect the consumption of a significantly greater amount of alcohol than that," he said.
Professor Forrest said the driver may have had as many as six drinks while off duty, as well as the two he was seen drinking by bar staff after being called back to the hotel.
He told the inquest: "If you said a litre of wine, that might be the sort of figure that would be a rough estimate of the amount of wine that he might have drunk between going off duty and coming back on duty."
When asked what effect the two drinks might have had on his ability to drive, Professor Forrest said: "I would not willingly have got in a car with someone who had two Ricards."
However, Professor Forrest did admit that his measurement was "imprecise" because of factors such as metabolism and the physical condition of the subject.
He said French authorities used the "gold standard throughout the world" for the measurement of alcohol in biological fluids and "did every test in the repertoire of the laboratory" on the samples.
Two French doctors - a toxicologist and a pathologist who were responsible for tests carried out on Mr Paul's body - have refused to come to London to give testimony at the inquest.
Blood test questions
Professor Forrest, a retired consultant in clinical chemistry and forensic toxicology, also said the body numbering for Mr Paul and Mr Fayed had been mixed up at one stage.
Princess Diana's death has been the subject of heated debate
The professor, who had made his own study of the case after seeing French medical papers relating to the deaths, used the phrase "garbage in, garbage out" to show how it was important to have "good quality samples you know the provenance of".
He told the inquest: "Bottom line is, the interpretation of the samples is only as good as the samples themselves.
"It doesn't matter how sophisticated the analysis is, if you don't have the good material to work with you have to qualify the interpretation of the data your laboratory generates."
Blood from the chest cavity could have been contaminated from the driver's stomach contents or his broken ribs, Professor Forrest said.
He said Dr Gilbert Pepin, responsible for the toxicology tests, believed the blood samples had come from Mr Paul's heart - but they had not.
"I was there when Dr Pepin was told it was not cardiac blood, it was chest cavity blood. I still have a vivid recollection of the way that his face changed when he was told, he looked surprised."
He added that a French medical paper showed five samples of blood were taken from the driver's body at the Institute of Forensic Medicine (IFM) in Paris during Mr Paul's post mortem.
Pathologist Professor Dominique Lecomte has said she took only three during the post mortem, and two more were later obtained by a colleague a few days afterwards.
The coroner has written to French authorities requesting Dr Pepin be compelled to attend the court hearing.