Ed Balls has turned against his "despicable" former colleague Damian McBride, and denied malicious briefing whilst in office.
The pair were both key members of Gordon Brown's inner circle whilst he was chancellor and prime minister.
Plugging his new book, McBride has spilled the beans on toxic infighting and the media manipulation with which he took down opponents within the party. He also accused Labour leader Ed Miliband of turning against him in an effort to further his own career.
The revelations have come at an inopportune time for Miliband, casting a shadow over the party conference in Brighton.
But Mr Balls has insisted that the party had changed under Mr Miliband's leadership.
The shadow chancellor told BBC1's Breakfast: "This kind of negative, nasty briefing is wrong. But I think also it's a thing of the past. The Blair/Brown era is gone. It is not how Ed Miliband and I are doing things in the Labour Party today. There's been none of it for the last three or four years. Thank goodness for that. We're in a better place now."
Asked whether he had ever briefed journalists against colleagues, he said: "That's not something I've ever done, I think it's the wrong way to do politics.
"Damian McBride has come out and said he did some of those things. It was despicable. It's the wrong thing to do."
Asked if he had used Mr McBride's services to undermine potential rivals during the party's 2010 leadership election, Mr Balls said: "If I ever did, it didn't work very well, did it? Because I didn't become the party leader.
"No, it's utter nonsense.
"There's always going to be people who will in an off-the-record smearing way make allegations, but it's not true and there's no evidence for that at all. It's not something I've ever done, it's not something I will ever do."
Mr McBride's book, Power Trip, is the first insider account of life inside Brown’s Treasury and Downing Street. He resigned amid scandal in 2009, when leaked emails suggested he planned spread false rumours about key Tory politicians, such as regarding their sexuality and fake allegations about their families.