The authorities reached their conclusion after tests on blood and other samples from his body appeared to show that he was three times over the French drink-drive limit.

But Dodi"s father, Mohamed Al Fayed, has always believed that the samples were faked or switched, pointing to question marks over the labelling of vials of blood, missing samples and doubts over DNA tests.

The coroner told jurors yesterday: "There is an issue about what part, if any, alcoholic drink played in the collision. Science should be the servant and not the master in situations like this."

He pointed to evidence that Mr Paul had definitely drunk two 5cl shots of Ricard " the equivalent of four single whiskies " in the Ritz Hotel in the two hours before he left on the fateful journey that also killed him.

But that would have still left him under the limit. It was possible, he said, Mr Paul had drunk more in the three hours he was off duty earlier in the evening.

The test results suggested he must have drunk the equivalent of up to six more Ricards. But the coroner said CCTV footage and most witnesses had suggested he showed no sign of being worse for wear.

It was regrettable, he said, that the French scientists, Prof Dominique Lecomte and Dr Gilbert Pepin, who tested the samples, had refused to testify to the inquest and answer severe criticism of the shoddy way they labelled and recorded their results.

He highlighted the inexplicably high levels of carbon monoxide in Mr Paul"s blood. "If the carbon monoxide readings must be wrong, what about the alcohol readings?" he asked. He also pointed out that while DNA samples sent from the French labs were shown to be from Mr Paul"s body, not a single one of them had also been tested for alcohol. The jury, expected to consider their verdict today, were also told other questions remained a mystery.

They include: How Henri Paul came to have such a large amount of money in his bank account, where he was in the three hours off duty, and who drove the white Fiat Uno that tests showed caught the Mercedes a glancing blow before it crashed into a concrete pillar.

The six women and five men jurors have been told to consider five verdicts. They include unlawful killing by Mr Paul or pursuing paparazzi or both; accidental death, or an open verdict.

There was insufficient evidence  of unlawful killing from a murder plot.

But the coroner has said that if they still suspect it might have been a staged crash, they should go for an open verdict.