Quote: Lord Mandelson has warned he will "ruffle some feathers" by publishing the inside story of the New Labour "soap opera" this summer.
The former business secretary has promised to lift the lid on what really went on between Tony Blair and Gordon Brown and said the book will offer a "mixture of history, autobiography and emotion".
He revealed he has regrets over helping create the pair's long-running feud by persuading Mr Brown not to seek the leadership in 1994.
"After (former Labour leader) John Smith died I was mistaken in arguing so hard that the two modernising candidates should not oppose each other," Lord Mandelson said.
"I did so from the best motives. I did not want two friends to hurt each other.
"I did not want the modernisers' cause damaged with the risk that a split vote might let in someone else.
"But if we had resolved the matter there and then, we would have avoided so much of the soap opera that followed."
He has refused to publicly endorse a candidate in this year's contest but, writing in the Times, called on the winner to make sure the party remains "aspirational, reforming, in touch".
Lord Mandelson also said electoral defeat killed off the era of politics he helped create.
"This phase of New Labour is now over and died on May 6, 2010," he said.
His book, The Third Man: Life At The Heart Of New Labour, will be published by HarperPress.
It hits shops before Mr Blair publishes his own version of events in a book called The Journey.
Lord Mandelson began writing his tome before his shock return to the Cabinet in 2008, when he was Britain's EU Commissioner. | 
