Lord Mandelson was reportedly paid around £350,000 by The Times for the serialisation rights to his memoirs.
The former business secretary is believed to have boosted the newspaper’s sales by more than 100,000 copies.
According to the Guardian, the newspaper achieved more than 35,000 sales last Monday and about 30,000 each on Tuesday and Wednesday, plus an extra 15,000 for Lord Mandelson’s editorial the preceding Saturday.
The newspaper reported that one source believed Lord Mandelson had earned up to £500,000 from the serialisation deal.
He is thought to have received an advance of £150,000 from Harper Collins for The Third Man, which recounts Labour’s years in power and the relationship between Tony Blair and Gordon Brown.
The memoirs have been attacked by leading Labour figures, including the five contenders for the leadership.
Diane Abbott called it “damaging”, David Miliband said it was “destructive”, Ed Balls called it “divisive”, Ed Miliband said it “offended just about everyone” and Andy Burnham called for Lord Mandelson to “leave the stage”.
Critics also suggested that the launch of the book, one month before Mr Blair’s, was a deliberate ploy to steal sales.
However, one source said to be close to the situation claimed: “I know that Tony and Peter are fine with it. The view is that Peter’s book is much more a domestic play, while Tony’s book is seen as also appealing to a much wider international market. He is still deeply popular in the US, for example.
“The only issue, and my understanding is that it is not a big one, is perhaps the frankness of what may be revealed about the Blair/Brown rift.”
Lord Mandelson told the BBC’s Andrew Marr yesterday that he had written the book for the “general voting public”, rather than Westminster insiders.