A report in The Sunday Telegraph says that Major Hewitt, 40, is talking to two newspapers about auctioning the serialisation rights to the book for more than �500,000.

It was understood that the Mail on Sunday was confident that it had secured the rights, before the News of the World almost doubled the offer, according to the report.

The Sunday Telegraph says that in the past, both newspapers have been "highly critical" of Major Hewitt's behaviour in making money from his relationship with the princess.

Princess Diana: Wrote love letters to Major Hewitt

The former Life Guards officer is reported to have written 60,000 words of the book so far. John Blake, a former editor of the People, is said to be conducting negotiations to sell the book, which Major Hewitt describes as his life story.

The report says that Mr Blake insisted the book would not include extracts of more than 60 love letters written by Diana to Major Hewitt.

The letters are now back in Major Hewitt's possession after he won a legal battle to retrieve them from the trustees of the princess's estate.

The Sunday Telegraph points out that copyright law prevents Major Hewitt from publishing the letters.

It quotes Mr Blake as saying: "The book is not just about his affair with Diana. It's his autobiography and it's a very good story. He was a war hero and very brave in the Gulf."

The money which Major Hewitt stands to make from selling the newspaper rights to his book will bring the amount it is estimated he has made from his affair to about �800,000, according to the report.