Ed Miliband has claimed Britain could slide into a "lost decade" because of the government's economic policies.
The Labour leader warned that public mistrust of politicians will be Labour's biggest challenge at the next general election.
Miliband spoke without notes
He insisted public anger with David Cameron and the coalition was growing in the wake of a no-change Budget, asking: "Can you imagine another five years of this?"
However, he also conceded that his party still has work to do to convince voters there is an alternative to grim austerity.
The comments came in an address to a 'people's policy forum' in Birmingham this afternoon.
It was followed by a Q and A session when he was put on the spot over Labour's policies on public sector pay.
One young man said to him he could not afford a flat, "but if I got someone knocked up tonight I could have a place tomorrow."
Miliband reeled off a list of policies that he claims would kick-start growth and make the economy fairer, including bank reform, infrastructure investment and a 10p tax rate.
He contrasted the platform he is fleshing out with George Osborne's financial package this week.
"All they offer is more of the same and that's not enough. Can you imagine another five years of this?
"Low growth. Living standards squeezed further. You paying the price.
"They are resigned to a lost decade. A lost decade Britain cannot afford. A lost decade of national decline.
"Not a decade where we make sacrifices now to build a better future, but where things get worse not better."
Miliband told the audience - billed as representing political opinion from across the West Midlands - that he had tried to understand the Labour government's mistakes on issues such as banking regulation, immigration and Iraq.
But he said there was now "an increasing disappointment and disillusionment with this Government" among the public.
"They don't believe David Cameron can turn Britain around," he added. "But let me be clear with you.
"I know that however discredited, divided and damaging this Government becomes, it doesn't necessarily translate into support for us.
"We have to earn your trust. Indeed, many people will believe that the failure of this Government means they should give up on politics altogether."
Conservative Party chairman Grant Shapps said: "Labour don't get it. They haven't learnt from their mistakes. All Ed Miliband offers is more spending, more borrowing and more debt - exactly how Labour got us into this mess in the first place."