Ed Miliband claimed today he was "winning the battle of ideas" but said it was a "hard process" to change the Labour Party.
The Labour leader said the party had "lost touch" with voters during the last government and that he and shadow chancellor Ed Balls had to demonstrate their "fiscal credibility".
But he dismissed criticism of his leadership as "part of the gig".
"You get criticism, you get advice, that's what happens," he told BBC1's Andrew Marr Show.
But he insisted that Prime Minister David Cameron was "coming on to my ground" on issues like taking on vested interests and "crony capitalism".
"What gives me confidence is that we are winning the battle of ideas. It's not often you say that about an opposition," he said.
"Why is he (David Cameron) coming on to my ground? Because he knows I'm talking about the right issues and the issues that matter to people.
"That's what gives me confidence."
He said the last Labour government had been "too soft on vested interests", had "got it wrong" on bank regulation and had not delivered a diverse enough economy.
But he went on: "We are changing the Labour Party and the process of change is always a hard process. I think we lost touch with people in government."
But he rejected the suggestion that Labour had spent too much when it was in office. "No. I'm not going to buy into the Tory myth," he said.
Asked about criticism from Labour peer and former adviser Lord Glasman, Mr Miliband joked: "I rather hanker for an elected House of Lords after Lord Glasman, but there we go."
Mr Miliband said he had agreed with Mr Balls to acknowledge the circumstances Labour would face if it were to win power in 2015.
But he insisted Labour still believed the Government was "cutting too far and too fast". If the Government "didn't change course", Labour would "inherit a difficult set of circumstances, he said.
Mr Miliband told the programme: "If Labour was in power now we wouldn't be making those changes, we wouldn't be cutting as far and as fast as the Government.
"We would be making cuts. So for example in the police we said that you could cut by £1 billion. We think you could protect frontline services but the Government decided to go further and faster.
"So when it comes to the next Labour government, if I was saying to you, 'I can absolutely promise to restore this cut or that cut', you would say 'Well, where is the money going to come for that? How to do you know? What circumstance you're going to inherit?'
"This is absolutely responsible opposition. And it is absolutely the right thing for us to be doing at this stage of the parliament."
Mr Miliband said the Government's current strategy was "self-defeating" as it had to borrow £158 billion more than anticipated.
The prospects for 2015 "looked pretty grim" as a result, he added.
Mr Miliband said it was right to protect jobs before guaranteeing to lift the public sector pay freeze.
In a speech yesterday, Mr Balls angered the unions when he effectively accepted the public sector pay freeze up to 2015, the year of the planned next election.
"I can't just promise to people that I can just wave a magic wand and be able to spend more and tax less," he said.
"I cannot make commitments now for three years' time. I won't do that, it wouldn't be credible."
Today, Mr Miliband said the stance was the right one to take.
He said: "In the end there are no easy choices for government and the choices for the next Labour government will be harder than they have been in the past.
"I think it absolutely right that we say that we prioritise employment."
Today, Bob Crow, general secretary of the RMT, said Labour's policy had "doomed it to electoral defeat".
He said: "Polls today show that support for Miliband and his policies has collapsed among labour supporters and the writing is on the wall.
"This isn't about personalities, it's about policies and the betrayal of those who expect the Labour party to support them when they are under attack."