Buckingham Palace admitted yesterday that it was powerless to take legal action against the former butler Paul Burrell for using private letters written by members of the Royal Family in his memoirs.
Lawyers for the Duke of Edinburgh are understood to have concluded that Mr Burrell and his publishers have adhered to copyright laws by only using extracts from letters written by Prince Philip, Diana Princess of Wales and her brother, Charles Spencer, among others.
The disclosure by Mr Burrell of sensitive personal correspondence, including letters from the Duke of Edinburgh making clear his disapproval of the Prince of Wales's adultery and a claim from Diana that there was a plot to murder her, has caused embarrassment and concern at the very top of the House of Windsor.
Penguin, which publishes Mr Burrell's book, A Royal Duty, on Monday, confirmed that an urgent request from the Palace to see the book on Tuesday had come directly from Prince Philip.
Joanna Prior, the publisher's head of marketing, said: "The Palace was in touch on behalf of the Duke of Edinburgh. It did not seem appropriate to hand over the whole book. We did, however, deliver by hand sections of the book referring to the Duke."
Royal officials had asked to see the book, which is being serialised in the Daily Mirror, after lawyers raised the possibility that Mr Burrell may have breached copyright. The copyright to personal correspondence rests with the writer or, in the case of the Princess, with their estate, meaning it normally can be reproduced only with the owner's permission.
But it is understood that the Palace's lawyers, Farrer & Co, have concluded that because Mr Burrell and Penguin have used limited extracts from the letters and acknowledged their source, they are unlikely to be in breach of the law.
Palace sources confirmed that the legal opinion made action on the question of copyright extremely difficult but said it was still waiting to see the full book before ruling out all court proceedings.
The third day of the book's newspaper serialisation was led by a letter to Diana from Earl Spencer in which he admits he had become estranged from her - a fact already made public at Mr Burrell's Old Bailey trial and subsequent acquittal on theft charges earlier this year. Writing in 1996, a year before the funeral address in which he eulogised Diana and castigated the Royal Family, Earl Spencer is claimed to have said: "I fear for you. I know how manipulation and deceit are parts of the illness [bulimia] ... I pray that you are getting appropriate and sympathetic treatment for your mental problems.
"I long ago accepted that I was a peripheral part of your life and that no longer saddens me. Indeed, it's easier for me and my family to be in that position as I view the consternation and hurt your fickle friendship has caused so many." The earl declined to respond to the revelations yesterday but told NBC television that the letter in which his sister had appeared to predict her own death in a car crash was merely a "bizarre coincidence" and not proof of a conspiracy. Asked about the letter to Mr Burrell in which Diana said she suspected a royal plot to tamper with the brakes on her car, Earl Spencer said: "With the conspiracy part of it, my family and I are absolutely certain that we have never seen any evidence of that whatsoever."
Michael Burgess, the royal coroner, responded to criticism that no inquest into the death of the Princess has been held. He said it could not take place until all legal proceedings in France had ended. "The inquest ... has not yet been held because the various investigations being made on my behalf have not so far been concluded," he said.
The outstanding legal actions are understood to include a complaint against a forensic scientist brought by the parents of the driver, Henri Paul, and proceedings for breach of privacy against several of the photographers chasing the car.