Ed Miliband is "struggling", according to former cabinet minister Peter Mandelson.
Speaking on BBC Radio 4's Today programme, the former business secretary said that the Labour leader was trying to create a new way of leftist thinking.
"What I think that Ed Miliband is doing, he's struggling with two things.. One is that he is trying to oppose the government on the economy where legitimately or not -people will take different views - they think the government's in the wrong place. But in making an argument against what the government is doing, fighting the recession, he's also struggling with his own inherited legacy from the previous Labour government and they're not doing that easily or finally, but nor is it simple to do.
"At exactly the same time he's struggling to invent a new left-of-centre political paradigm that isn't new Labour."
He added: "He's trying to do these things simultaneously. Neither of them are simple or straightforward at a time when not many people are giving him the benefit of the doubt. It's a rather unenviable job."
And Mandelson, who served in the Cabinet under Blair and Brown said: "The centre-left have got to fight back. But not by reverting to old arguments about state control and intervention. And not, in my view, by using, employing, too much of the new rhetoric on the left of business and bank bashing. I don't really think that will get them anywhere at all."
Lord Mandelson also disowned his comment about being "intensely relaxed" about people becoming filthy rich "as long as they pay their taxes". He said on Thursday: "I don't think I would say that anymore... We've learnt that markets whilst indispensable to global growth can become volatile and unstable and have to be managed and regulated."
Mandelson also praised the coalition's ministers, saying universities minister David Willetts gave a speech recently that he could have "written every word of".
"I'm actually very proud and pleased with what BiS is doing. After a shaky start BiS has got into its stride. If you see what Vince Cable is doing, what David Willetts in particular, the higher education and science minister is doing.. In a sense taking to a higher an more sophisticated level the sort of industrial policy thinking and actions that I was introducing when I came back into government."
Conservative Party Co-Chairman, Baroness Warsi, said Ed Miliband was "simply not up to the job": “It’s unsurprising that Peter Mandelson, the co-architect of New Labour and a man who knows how to win elections, thinks that Ed Miliband is ‘struggling’."