David Cameron has accused the Government of putting "naked political calculation" ahead of Britain's economic interest by failing to promise immediate public spending cuts.
The Tory leader said it was "good news" that official statistics are expected to confirm on Tuesday that Britain is out of recession.
But he said that would mean nothing without urgent action to tackle the £178 billion budget deficit, warning that the UK was borrowing £6,000 a second.
The Opposition have said they would impose cuts in a post-election emergency budget and Mr Cameron, at his regular press conference, said it was time for Labour to "do the right thing".
"Our recession, the great recession, is the longest and deepest since the war and coming out of recession does not mean that our debt crisis is over," he told reporters.
"In fact far from it: Labour's debt crisis is now the biggest threat to our recovery so we will only get this recovery right if we start right now on a proper debt reduction plan."
Britain was borrowing more than Greece, whose debt had already sparked the sort of economic crisis that could see soaring interest rates and unemployment if repeated here, he said.
"The Government's promise to halve the deficit in four years has frankly failed to convince those who we need to have confidence in Britain's economic future.
"A key part of any plan is at least some early action to show you are serious in your intent. That means some reduction in public spending plans in this coming financial year. The Government's approach, to coin a phrase, is to do nothing.
"If we are going to have to wait for May for an election and if there is going to be a Budget in March, they need to show how they are going to start now. They are about to tell us that the economy is growing so they have no further excuse to delay action except naked political calculation."