Stevens faces questions about 'discrepancies' surrounding Diana's death

Fresh doubts about Henri Paul - said to have been three times over the alcohol limit when their car cashed in a Paris tunnel - were raised by lawyers for his family at a preliminary hearing of Diana's inquest yesterday.

At the High Court, they said the conflicting evidence fuelled allegations of a "cover-up" over her death.

At the same hearing the coroner, Lord Justice Scott Baker, outlined 20 questions which he said would help him make a decision on whether the princess was murdered, as Mohamed Al Fayed has claimed.

He said he would attempt to explore all the questions during the six-month inquests into the deaths of Diana and Mr Al Fayed's son Dodi in the 1997 Paris crash.

Richard Keen, QC, for Mr Paul's family, called for Lord Stevens, who headed the Operation Paget inquiry into Diana's death, to become a witness.

He said Lord Stevens had told Mr Paul's parents their son was not drunk at the time of the crash, then a month later concluded in the Operation Paget report that he was three times over the French alcohol limit.

Mr Keen told the court: "What we need to know is why is there such a gross discrepancy between what he was saying on November 9 and what was published on December 14.

"The gross discrepancy highlights the allegation that there has been a cover-up."

Mr Keen said the conclusion of the report could have been 'materially altered' so as to pin the blame on Mr Paul, "a convenient scapegoat".

The coroner confirmed that Lord Stevens would be asked about the matter and that he was a possible witness.

Mr Keen also raised fresh questions about Mr Paul's blood samples. He claimed experts now agreed that a prescribed drug Mr Paul had been taking was not found in his the samples, but one he had not been prescribed was discovered.

Mr Al Fayed's QC Michael Mansfield repeated calls for the Queen to be asked about claims she had told royal butler Paul Burrell there were "powers at work in this country about which we have no knowledge".

But the coroner refused, saying: "It has absolutely no relevance whatever. Someone's got to draw a line."

The full inquest is scheduled to start on October 2.