Morton has written 16 books including royal biographies

The pop icon was livid that he wrote it without her permission, saying: "It's not a well-written book. We all know he wrote it for financial gain and the truth had little to do with it."

But Morton remains unabashed.

He wrote it because of his interest in the star, not least because she has made a "difference" to pop culture and modern culture.

Morton, who started his career as a journalist who worked on the royal circuit, insisted Madonna is more than just tabloid fodder, adding she has been described as an "icon of post modernity".

And he is convinced his hard work has paid off, saying: "I'm very proud of the book and I'm very disappointed at Madonna's reaction.

His book about Diana was reissued after her death

"I think the problem is that she wants control over everything - that's one of the themes of the book, and secondly she seems to be almost disowning her past at the moment.

"She's reinventing herself as an upper-class, English aristocrat, the former vegetarian who now goes hunting, fishing and shooting."

Offering an olive branch, he added: "My door's always open - Madonna's welcome to my house for a cup of tea."

No doubt he would be charming - a vital attribute for a biographer needing to get people to open up and talk about themselves and other people.

The Beckhams did not endorse Morton's book

I discovered Morton's charms for myself after being greeted with a string of compliments about the colour of my eyes when we met - an unusually bold move for someone about to be interviewed.

But he was serious enough while talking about his career and his books, detailing his "detective work" researching Madonna's life in New York, where she clambered her way up to fame and fortune.

"Not only is she an interesting character, but all her friends and those who've known her are interesting characters too," he said.

"So I've spent a lot of fun evenings in bars and clubs in New York chatting to people - some of them are artists, musicians, directors - they have an interesting perspective not just on Madonna but on the world."

Monica Lewinsky worked with Morton on her biography

Morton interviewed about 70 people who had known the star since her youth.

"I think I've come up with a very fresh picture," he said, adding that Dan Gilroy, who "introduced" Madonna to music, had e-mailed him saying it had "really captured Madonna's spirit".

The book is certainly detailed, and will no doubt keep Madonna fanatics happy, although it is perhaps more of a reference book than a page-turner.

But Morton is a good businessman, and is canny in his choice of subjects.

They are all globally famous, and apart from Kenyan president Daniel arap Moi, they are regularly splashed across the front pages of the tabloids, guaranteeing public interest in them.

Diana's death

Morton appears to have no qualms writing about their private lives, because they have already put themselves in the public arena.

But in the case of Diana, he did not reveal she had collaborated with him over her biography until after her death in 1997.

Why do this at such a sensitive time - and spark the inevitable criticism that he was just out to make more money?

"There was never any intention to reveal her collaboration until after my death, and in fact all the papers are in my will to go to my old university," he said.

Film

"But after her death there seemed to be no point in maintaining the charade. There was no real advantage other than to set the record straight," he added, omitting to mention that a revised version of the book was reissued after Diana's death.

Morton himself has been the subject of a biography of sorts - a film called The Biographer starring Paul McGann.

He does not know if the film will ever be released, saying he knew it had been made a couple of years ago.

Without a trace of irony, he added: "I was interviewed by the scriptwriter, but whether it bears any relation to what happened - I don't know."

No doubt he will have to trust that the film-makers have got their facts right.