Diana driver samples questioned

Henri Paul's body showed high levels of carbon monoxide, the court heard

Problems with the blood samples from the body of Princess Diana's driver suggest a "conspiracy or a cock-up", a toxicologist has told her inquest.

Professor Robert Forrest said "biologically inexplicable" levels of carbon monoxide in Henri Paul's blood were "analytical error or a mystery".

He said if the Ritz security chief had been exposed to that level of the gas, he would have appeared ill.

He also said there were no signs of two medications Mr Paul had been taking.

Princess Diana and her companion Dodi Al Fayed died with Mr Paul in a car crash in Paris in August 1997.

This is the one thing which worries me most about this investigation Professor Robert Forrest

Professor Forrest said he had watched CCTV footage of Mr Paul in the Ritz the night of the crash. He said the driver was walking around, laughing and tying his shoelaces with no apparent sign of any ill effects.

It was "very, very unlikely" Mr Paul had a 20.7% Carboxyhaemoglobin concentration, as found in post-mortem tests, he concluded.

"This is the one thing which worries me most about this investigation," he told the court. "I still have not managed to achieve an intellectual resolution which satisfies me."

He said to the court: "I look to the jury (to decide) - conspiracy or cock-up?"

He said there was no indication of similar Carboxyhaemoglobin concentrations affecting Mr Fayed or Princess Diana.

Professor Forrest said the machine used to measure blood gas was a "good piece of kit", but it was not intended to be used in post-mortems.

One explanation is that the two samples did not come from the same source Professor Robert Forrest

"One is left with either analytical error or a mystery," he told the inquest's jury.

"One explanation is that the two samples did not come from the same source," Richard Keen QC, for Mr Paul's family, said.

Prof Forrest answered: "That, I accept, is a possible explanation which could be addressed by various means."

Mr Fayed's father, Harrod's owner Mohammed, alleges samples were mixed-up in order to disguise a murder plot.

The court has heard on Monday that medical tests showed Mr Paul was twice the legal UK drink-drive limit the night of the crash.

Professor Forrest said this was consistent with eight drinks of the liqueur Ricard. Mr Paul was said to have had two 50 ml measures of the drink while on duty at the hotel.

The inquest continues.