Professor Thomas Treasure, a former president of the European Association for Cardio-thoratic Surgery, said that French medics who arrived at the scene of the accident had done "very substantial good, " but time began to "slip away" once Diana was in the ambulance.

He told the London jury that the princess could have survived if the journey to the hospital had been short, if a specialist team had been on standby, and if a surgeon had taken the decision to open up Diana's chest from the front rather than the side.

French doctors said that without their actions Diana would have been dead on arrival because she was so fragile.

But Professor Treasure said the Princess had been successfully stabilised soon after being put into the ambulance and could have been taken to hospital then.

"They had done a lot of good in that first half hour but from here, the next big amount of good that could be done required a surgeon, " the Daily Mail quoted Prof Treasure, as saying.

Inquest lawyer Nicholas Hilliard asked him: "Is it your view that part of that time, the essential period, was squandered? "

He replied: "It's a hard word, isn't it, but I think opportunities were lost... when I pick through this with the benefit of hindsight (and ask) 'was this recoverable? ' the answer is 'yes, it just about was. '"

He also questioned the decision of a French doctor in Diana's ambulance to order the driver to go slowly and then to stop for a full five minutes when it was just a few hundred yards from the hospital.

The London inquest has heard that this was because the medic feared her pulse was about to stop for a second time and wanted to keep her stable.

But Professor Treasure said: "Whether, within a minute of the hospital, you would put your foot on the accelerator or on the brake is open to some debate. "

He also said that the surgeon who operated on Diana should have opened her chest from the front rather than the side, which might have allowed him to identify the source of her internal bleeding more quickly.

And he said the "extraordinary" amount of adrenaline Diana was given during the surgery might have been counterproductive.

The inquest was also told that Diana was so agitated after the crash she had to be restrained. At one point she was shouting out in English, thrashing around and even pulled out a drip.

Professor Andre Lienhart, who investigated Diana's treatment for a French probe, earlier told the inquest that she was "agitated", had "refused treatment" and pulled a drip out of her arm while being treated in the Pont de l'Alma tunnel.

Diana, her boyfriend Dodi Fayed and their chauffeur Henri Paul were all killed in the crash on Aug 31 1997. (ANI)