Diana inquest: Crash caused by Henri Paul's 'overzealous' bid to avoid white Fiat Uno

Accident expert Tony Read, the senior British collision investigator in the case, said evidence showed that the Princess's Mercedes clipped the rear of the Fiat entering the Pont de l'Alma Tunnel in Paris in the early hours of August 31 1997.

But he said that it was Henri Paul's "overzealous" steering rather than the "glancing" contact itself which appeared to have led to the fatal crash.

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Showing diagrams of tyre tracks recorded at the scene, he said the Mercedes had gone left, then right, then left again before crashing into the 13th pillar of the tunnel at 60-70 miles per hour.

Debris suggests that the Mercedes clipped the rear of the Fiat about 10 metres outside the entrance to the tunnel - rather than inside, he said.

"It was the presence of the Fiat that required Henri Paul to steer left," he told the court.

"It was probably as a result of an over-reaction, maybe a slightly overzealous application of the left steer that meant that he had to steer to the right in order to avoid the central reservation.

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"That in turn meant he had to steer left to avoid a collision with the tunnel wall and that in turn meant that he was unable to control the vehicle and collided with pillar 13."

But he said there were several factors he believed played a part including:

• Driver impairment through drink or drugs.

• The distraction that may have been caused by the paparazzi.

• The excessive speed of the vehicle.

• The presence of another vehicle and the requirement to take avoiding action.

• Unfamiliarity with the Mercedes (which was not Henri Paul's usual vehicle).

• A challenging road lay-out.

• The "stress or euphoria" of the situation.

The court heard that it was unclear whether the Fiat had been travelling on the expressway ahead of the Mercedes or emerged from a sliproad just before the tunnel.

But based on the speed the Mercedes was travelling at and Henri Paul's likely reaction time, Mr Read calculated he would have spotted the white car about 78 metres before the first set of tyre tracks - just at the point the sliproad joins.

The jury heard that under French law cars must give way to vehicles on the right meaning that those coming from the sliproad would technically have right of way over those on the expressway itself.

Last week the jury heard a statement from witness Jean Louis Bonin who described the junction as "the most dangerous in Paris".

In a seperate development the coroner ruled today that transcripts of police interviews with paparazzi who are refusing to attend court can be admitted in evidence.

The ruling, a blow to Mohamed al Fayed, allows the inquest to continue after the French government decided not to force the photographers, who pursued Diana to the scene of her death, to give evidence by video link from Paris.

But coroner Lord Justice Scott Baker said lawyers for Mr al Fayed and others would be allowed to object to the documents on a "witness by witness basis" - raising the prospect of further legal wrangles as the case goes on.

The French decision, in the face of high level calls from London for a rethink, threatened to prevent the jury hearing any evidence from the crucial paparazzi witnesses.

Lawyers for Mr al Fayed - whose son Dodi died in the crash which killed Diana in 1997 - his Ritz Hotel in Paris and the family of his former employee driver Henri Paul, all objected to transcripts of the paparazzi interviews with police and other potentially controversial written evidence being read out without a challenge.

Richard Keen QC, representing the Paul family, supported by Michael Mansfield QC for Mr al Fayed and Ian Croxford QC for the Ritz, argued last week that doing so would give lawyers no opportunity to cross-examine anyone about possible inconsistencies in the paparazzi accounts.

They argued that the Coroners' Rules 1984 did not allow for such evidence to be admitted because it was not "unlikely to be disputed".

In a ruling published today, Lord Justice Scott Baker conceded that the rule concerned was "far from clear". But he announced that the evidence could nevertheless be admitted under established law.

He said he had sought to take a "liberal approach" to questions of calling evidence because of the unique nature of the inquest being heard at the High Court.

"The reason for that is that one of the purposes of these inquests is to confirm or allay public suspicion," he said.

He went on: "It seems to me that where possible the jury should hear relevant evidence on all issues that remain live even where the witness is unwilling to give it orally."

He said that in the light of that approach it would be "inconsistent and wrong" to be restrictive with evidence from people who refused to be cross-examined in person.

"In these inquests above all others it seems to me particularly undesirable to leave issues in the air if there is evidence that might resolve them one way or another," he said.