Queen's former private secretary 'was being entertained by John Mortimer' on night Diana died

The Queen's former private secretary had a cast-iron alibi on the night it was claimed he was in Paris helping to arrange the murder of his sister-in-law, Diana, Princess of Wales.

Lord Fellowes, who is married to Diana's sister, Jane, told the High Court in London that he could not have played any part in arranging the car crash that killed Diana and Dodi Fayed because he was in a church hall in Norfolk listening to a talk given by the author John Mortimer, the creator of Rumpole of the Bailey.

Dodi's father, Mohamed Al Fayed, has alleged that Lord Fellowes co-ordinated the "conspiracy" by commandeering a section of the British embassy in Paris to send messages to GCHQ shortly before their deaths on 31 August 1997.

Ian Burnett QC, counsel to the inquest, told Lord Fellowes: "It had been suggested, particularly in a letter from Mr Al Fayed, that it was said that you had been present in the British embassy at 11 o'clock on the evening of 30August, 1997, commandeering the communications centre to send messages to GCHQ." He added: "In other words it was being suggested that you were intimately concerned in the murder of your sister-in-law. You understand that that was the allegation?"

Lord Fellowes nodded.

Asked if he had been in Paris that night he answered: "No."

He then added: "We were in Norfolk that evening; we had people to stay. We went to an entertainment by Mr John Mortimer in Burnham Market church."

Lord Fellowes also claimed the Royal Family did not direct any animosity towards Diana.

Mr Burnett told him: "It has been suggested in that period and later the Duke of Edinburgh displayed animosity towards the Princess of Wales in writing and more generally." Asked if he had ever spotted such a reaction to Diana, Lord Fellowes replied: "No, I never saw that."

Giving evidence to the inquests of Diana and Dodi Fayed he also revealed that rooms at Buckingham Palace were regularly swept for bugs by MI5. He said the security service conducted the sweeps in rooms used by the Queen and her private secretary to conduct business to provide "reassurance".

The revelation emerged during questioning about the notorious "Squidgy-gate" and "Camilla-gate" tapes – recordings of telephone calls involving Diana and the Prince of Wales. Lord Fellowes told the court how the recordings – which were revealed in the press – prompted high-level meetings and correspondence involving the heads of MI5 and GCHQ, the Government's listening station, in early 1993.

But the then home secretary, Michael Howard, said Lord Fellowes, blocked a full security service investigation for fear that such a move would leak and be misrepresented in the press.

Among the documents shown to the court were letters between officials at the time that explained these concerns. One was a letter from Sir Clive Whitmore, the Permanent Secretary at the Home Office, to the then Cabinet Secretary, Sir Robin Butler (now Lord Butler). It read: "He [the Home Secretary] thinks that there is a real danger that even a security service inquiry of the kind we have in mind would quickly come to the attention of the media.

"His strong fear is that when that happened, the press would portray the existence of the inquiry as clear proof that... they believed in fact that such involvement was a real possibility and that they were therefore having it investigated."

Lord Fellowes also told the court that the recordings had caused concern at Buckingham Palace. He said: "It would be wrong, I think, to say that the Queen 'demanded an inquiry' – it wasn't her habit to react in that way but to consult and to be informed by the best advice available. We needed reassurance at regular intervals that there was no bugging going on.

"There were two strands of thinking, one was obviously if there had been anything nefarious done that it should be discovered and punished. But the main strand of thinking in Buckingham Palace... was that this had happened and what action should be taken to ensure that it did not happen again."

The hearing continues.