When it was published five years ago, Diana - Her True Story caused a public furore and made a fortune. The updated version, due out on Monday, is proving almost equally controversial and could lead to legal action from the executors of the late Princess's will. It will also prove very lucrative for Morton and his publishers.
The first wave of condemnation came last week over Morton's announcement that the original book had been in Diana's own words and was in effect her autobiography.
But the fresh revelation that Morton has sold the transcripts of his interviews with the Princess to an American magazine, People, for more than pounds 100,000 has produced even greater outrage.
The 18,000 words, spoken by Diana on to a tape at Kensington Palace and then passed to Morton by an unnamed intermediary, formed the basis of his original book but have never before appeared in publicly available print. Extracts will appear in the new book.
They are said to form a devastating and intensely personal account of the Princess's engagement and marriage to Prince Charles; all in her own words.
Although the transcripts provide little new of substance, the shock comes in reading the bitterness of Diana's own words in criticising her husband and family.
Critics, who include MPs, churchmen and - reportedly - members of the Royal Family itself, criticise Morton for cashing in so soon after the Princess's death and of subjecting her children to yet more details of their parents' unhappy marriage.
Diana's executors, who include her sister Lady Sarah McCorquodale and their mother Frances Shand Kydd, have now taken legal advice about whether they can stop publication of the transcripts and the updated book Diana: Her True Story - In Her Own Words.
Yesterday, there was no comment from the Princess's office at Kensington Palace, but legal experts thought that while Diana may retain copyright in her own words, it was an arguable case.
The feeling was that the uncertainty of the legal status of her words - handed with her permission on tape to Morton - and the risk of prolonging publicity by taking the matter to court would dissuade the executors from action.
In any case, it may be too late - early copies of the book are on sale in central London and People magazine is already on the news stands.
Last night, Earl Spencer and his family were still consulting with lawyers on "various points" and were said to be "very distressed and saddened" by the publication of the book.
Morton himself was unrepentant yesterday. Clearly irritated by the personal attacks from tabloid newspapers which have in the past fed off his words, he accused his detractors of hypocrisy.
Saying that he was proud to have been chosen to write the book, he added: "I think I have behaved extremely honourably throughout this episode."
Mr Morton, who is said to have made pounds 4.5m from the original publication, defended making the transcripts public while Diana's young sons were still grieving.
"If they really wanted to understand their mother, they would want to read her words," he said. He also denied selling the entire tapes to People magazine - insisting it was just "extracts from the new book". The author described Diana's words as "her legacy, her final testament".
Leading article, page 20Reuse content