Lord Mandelson has criticised Ed Miliband's energy plans, saying he risks taking the party backwards.
The former business secretary, who in 1997 helped mastermind New Labour's triumphant election campaign, said Mr Miliband's pledge to freeze energy bills could undo the industrial policy he had worked hard to shape under Tony Blair.
He said: "At the business department I tried to move on from the conventional choice in industrial policy between state control and laissez-faire. The industrial activism I developed showed that intervention in the economy - government doing some of the pump priming of important markets, sectors and technologies - was a sensible approach."
But following Mr Miliband's speech yesterday at the party's annual conference, he added: "I believe that perceptions of Labour policy are in danger of being taken backwards."
Energy companies were unsurprisingly united in their criticism of the Labour leader's announcement in Brighton, which went down well with the party's grassroots.
But another fellow New Labour architect Alastair Campbell disagreed with Lord Mandelson.
The former director of communications said in a tweet: "Peter M wrong re energy policy being shift to left. It is putting consumer first v anti competitive force. More New Deal than old Labour."