Mohamed al Fayed disputes the findings that Henri Paul had been drinking on the night of the crash.

The Harrods owner - whose son Dodi was killed along with Diana and Mr Paul - believes samples may have been switched at the Paris morgue to cover up a murder plot orchestrated by intelligence services.

The court heard today that Mr al Fayed dispatched Prof Peter Vanezis - who was then professor of forensic medical sciences at Glasgow University - to Paris two days after the crash hoping to do a second post-mortem examination on Mr Paul’s body.

The jury was told that he was refused permission by the French authorities but was later given pathologists’ reports to analyse.

Professor Vanezis also raised concerns about the quality of the initial blood test taken from Mr Paul’s body.

But he was later given results of analysis of other samples including hair and vitreous humour which pointed to Mr Paul having been drinking.

Prof Vanezis - now of Barts and the London (Queen Mary University of London) - later produced a joint report with forensic toxicologist Prof John Oliver, Swiss forensic pathology professor Thomas Krompecher and Patrice Mangin, professor of legal medicine at Lausanne University.

They concluded: “Looking at the overall picture, it may be fairly clearly observed that Mr Paul had an alcohol problem and he drank high levels of alcohol regularly.”

Giving evidence today, Prof Vanezis explained: “One of the things obviously we were considering, and obviously this was very much at the top of our minds, was whether or not that person that appeared normal in the CCTV images may well have built up a tolerance to alcohol.”

The report adds: “There is no doubt that the average man’s faculties would have been markedly impaired but a regular drinker like Mr Paul is likely to have been impaired less.”

** Read the very latest on the Princess Diana inquest now **