David Cameron's plea for "responsible capitalism" is failing because he wants to do it by asking businesses to behave better rather than changing the rules, Ed Miliband has claimed.
The Labour leader highlighted Mr Cameron's famous 2006 attack on WH Smith for stocking chocolate oranges rather than real oranges by the tills which he said had no impact on retailers' behaviour.
The Prime Minister's decision to appeal for moral capitalism in a high-profile speech last week was a sign that Labour was "shaping the battle of ideas" after he identified the issue in his conference speech four months ago, said Mr Miliband.
The Labour leader told The House magazine that, six years after Mr Cameron criticised point-of-sale discounts on chocolate oranges, the tactic was still being used by retailers.
Mr Miliband added: "If he can't sort out the chocolate orange, he's not going to be sort out the train companies, the energy companies, the banks, is he? I think it's very interesting that David Cameron's example of responsible capitalism was the chocolate orange.
"He's failed to sort it out. Why? Because of his basic set of beliefs. You know, he believes in a nudge philosophy which seems to amount to just asking people to do nice things. But that isn't going to sort out the problem. You've got to change the rules."
Mr Miliband said he faced a lot of criticism for taking on "predatory capitalism" in his conference speech last September.
But he added: "Three or four months later, (Nick) Clegg and Cameron are saying `We're sort of on the same page'. That tells you something about them knowing that I'm making the right arguments. Labour is shaping the battle of ideas and that is really important because I don't think we were doing it at the last election."
Mr Miliband also said he believed Labour's message on the economy was getting through to ordinary voters, who were beginning to quote back to him his analysis that the Government was cutting "too far and too fast".
He defended his controversial decision to back the Government's public-sector pay squeeze, which provoked what he suggested was a "watershed" row with unions.