Mohamed Al Fayed’s personal security chief admitted yesterday to lying in public, as he was cross examined in the inquest of Diana, Princess of Wales.

John Macnamara, a retired Scotland Yard detective chief superintendent, conceded that he had told less than the whole truth about Henri Paul, who was driving on the night of the fatal crash in 1997, in an interview to ABC television ten days later.

He told viewers that Paul had been drinking only pineapple juice when he knew that he had consumed at least two Ricard spirit drinks in the bar of the Ritz Hotel in Paris.

At the inquest yesterday, in which Mr Al Fayed claims that there was a conspiracy to murder his son, Dodi, and the Princess, Mr Macnamara, who headed Mr Al Fayed’s private investigation into the crash, said that he believed that his duty had been to assist the French police in their inquiries, and that he did not necessarily want to share information with anyone else.

His explanation failed to impress Lord Justice Scott Baker, the coroner, who asked Mr Macnamara: “Was it the whole truth, what you said in the interview?”

Pressed, the witness conceded that it was not.

“So it was not the whole truth,” the coroner said. “As a former chief superintendent surely you, above anybody, are aware of the importance of telling the truth in public? So a half-truth is good enough. The public can learn half the truth but not the whole truth.

Mr Macnamara, a problem for the jury is that, if you tell lies on some occasions, how can they tell if you are telling the truth on others?”

The witness said that he had come to the inquest to tell the truth.

It was not the first mauling that Mr Macnamara had had from the coroner. Earlier, evidence was produced of a statement issued by Mr Macnamara refuting sections of a book written by Trevor Rees, the bodyguard who survived the crash despite severe injuries.

The statement alleged that Mr Rees, then known as Rees-Jones, had taken money to be a mouthpiece for the security services “to discredit the mounting evidence that the crash was not an accident”. Mr Macnamara was asked if he had taken any steps to apologise to the bodyguard. No, the witness replied. “Why not?” the coroner demanded. “I have not seen Mr Rees. The statement was my belief at the time,” Mr Macnamara replied.

The witness sailed into further trouble over a statement he had made and signed saying that he had identified Mr Fayed’s body when it was brought back from Paris to Fulham mortuary in West London. Yesterday, he retracted this, saying that he had only read out the full name of the deceased from his passport to assist officials.

Mr Macnamara claimed that as he waited for Mr Fayed’s body to be returned he had received a telephone call from Michael Burgess, the Surrey Coroner, informing him that the body would be delayed because he had heard from Scotland Yard that there could be suspicious circumstances surrounding the deaths. Both Mr Burgess and the Metropolitan Police have denied that any such conversations took place.

Cross-examined by Richard Horwell, QC, for the Metropolitan Police, Mr Macnamara could offer no evidence to support a conspiracy to murder that involved the Duke of Edinburgh, the British and French security services, the French medical services, the Surrey Coroner, Lord Condon, the former Metropolitan Police Commissioner and Peter Jay, the British Ambassador to Paris at the time. Nor could he offer any evidence to support claims that the Princess was pregnant, or was about to become engaged to Mr Fayed.

The hearings will continue on Monday.

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