Peter Mandelson, the former business secretary, has announced his plans to publish an autobiography this summer.

The gay peer promised today that the book would “ruffle some feathers” and give his view of the relationship between Tony Blair and Gordon Brown during the last 13 years.

He said the title would be ‘The Third Man: Life At The Heart Of New Labour’ and he is said to have secured a six-figure advance for the work.

Lord Mandelson wrote in the Times: “The book contains a mixture of history, autobiography and emotion. It will be my story of a life played out in the back room, then on the front line of the Labour Party, and in our unprecedented three terms in government.

“It tells it as I saw it, working off the detailed notes, papers and diaries that I kept throughout my career.

He added: “It will no doubt ruffle some feathers but if it didn’t it wouldn’t tell the story of what New Labour achieved in government, where and why it didn’t achieve everything that we hoped for, and what it can accomplish in the future.”

Lord Mandelson has been a controversial figure for years, having acquired the nickname ‘the Prince of Darkness’.

He was twice forced to resign from the Cabinet during Mr Blair’s premiership over his business dealings but returned to politics in 2008 to accept a seat in the Lords and become deputy prime minister in all but name.

He was famously outed on Newsnight in 1998 by gay journalist Matthew Parris and two years later, allowed himself to be photographed in public with his long-term partner Reinaldo Avila da Silva.

Unlike many other out gay politicians, Lord Mandelson has never spoken publicly about his sexuality and has consistently rebuffed interview requests from the pink press.