Princes William and Harry launched a ferocious attack on former royal butler Paul Burrell last night accusing him of a "cold and overt betrayal" of their late mother.

Diana, Princess of Wales, would have been mortified at his revelations if she were still alive, the brothers said.

Mr Burrell, who worked closely with the princess, has published a series of claims from his new book in a newspaper.

He fuelled conspiracy theories surrounding her death by writing that Diana feared for her life and spoke of a plot to tamper with her car's brakes.

William, also speaking on behalf of 19-year-old Harry who is in Australia as part of his gap year, described their deep pain at the stories and appealed to Mr Burrell to end his allegations.

Royal officials said the princes would be prepared to meet Mr Burrell to discuss the matter.

In a statement, unprecedented for its strength of feeling, William, 21, said: "We cannot believe that Paul who was entrusted with so much could abuse his position in such a cold and overt betrayal.

"It is not only deeply painful for the two of us but also for everyone else affected and it would mortify our mother if she were alive today and, if we might say so, we feel we are more able to speak for our mother than Paul.

"We ask Paul, please, to bring these revelations to an end."

But last night Mr Burrell refused to apologise for the book and insisted the public should know the truth.

In extracts from his book, published in the Daily Mirror, Mr Burrell claimed the Duke of Edinburgh wrote to Diana telling her he and the Queen "disapproved" of the Prince of Wales's affair with Camilla Parker Bowles. It was reported that the Duke told Diana: "I cannot imagine anyone in their right mind leaving you for Camilla."

Much of the book appears to be based on letters written and received by Diana, as well as Mr Burrell's experiences and observations as the Princess's butler and confidante.

Mr Burrell also said that Earl Spencer, Diana's brother, wrote to his sister expressing concern for her mental health, saying: "I know how manipulation and deceit are parts of the illness".

The Earl said he was angry the private correspondence was published, adding also that he had never seen anything to suggest the crash in which his sister died was anything but an accident.

In the latest revelations, it was alleged that Diana had nine secret "gentleman friends" including a Hollywood star, a sports legend, a leading musician and a famous politician.

A Clarence House spokeswoman said the statement was aimed at drawing the line: "It's telling Paul Burrell that they've had enough."

Mr Burrell was cleared last year of stealing hundreds of items from the late Princess's estate when his Old Bailey trial collapsed dramatically following an intervention by the Queen.

It is believed lawyers acting for the Royal Family are unlikely to take action over the book. It is understood Mr Burrell and his publishers may have slipped through a legal loophole to escape censure.

The reports that Diana feared a plot have led to claims that the French police are considering reopening the investigation into the 1997 crash in Paris which killed her and boyfriend Dodi Fayed.

Last night, Mr Burrellsaid: "I am saddened at the statement issued on behalf of Prince William and Prince Harry. Saddened because I know that this book is nothing more than a tribute to their mother.

"I am convinced that when the princes, and everyone else, reads this book in its entirety they will think differently. My only intention in writing this book was to defend the Princess and stand in her corner.

"I would also like to point out that, following the collapse of my trial, no one from the Royal Family contacted me or said sorry for the unnecessary ordeal myself, my wife and my sons were put through.

"Neither do I say sorry for writing this book of which I am extremely proud and I am convinced the Princess would be proud of too."