Lawyers for Mohamed al Fayed last night launched a bid to involve the Queen in the Diana, Princess of Wales inquest.
They want the monarch to be "directly approached" over claims she told Princess Diana's former butler Paul Burrell that there were "powers at work in this country which we have no knowledge about".
Mr Burrell alleged after the collapse of his Old Bailey trial for theft in 2002 that the Queen issued her warning to him shortly after the Princess's death.
Michael Mansfield QC, representing Mr al Fayed, whose son Dodi was killed alongside Diana in 1997, called for the Queen to be contacted about the matter.
His request came during the first preliminary hearing for the inquest since Lady Butler-Sloss made the shock announcement last month that she is to quit as coroner in June. Mr Mansfield said: "The inquiries which we suggest be made to assist is for Her Majesty being directly approached and asked was there evidence of conversations as alleged by Mr Burrell?"
Lady Butler-Sloss said: "In as far as you're saying that Her Majesty should be directly approached, I think that's unheard-of." She said they should tread carefully over what could be a constitutional matter.
Buckingham Palace declined to comment.
A spokeswoman said: "It's a matter for the Attorney General, who is representing the Queen's interests as monarch."