Labour leader Ed Miliband has said that the government's economic strategy is locking Britain into a "vicious cycle on the deficit".
In a speech in London, he said next week's autumn statement will show their plan "has failed" and confirm a further rise in borrowing.
Flat growth and high unemployment means it is time to change course, he says.
Prime Minister David Cameron says Labour plans to spend more are the "height of irresponsibility".
Mr Miliband told the IPPR think-tank that next Tuesday's autumn statement - in which Chancellor George Osborne will present the official economic and public finance forecasts - will "mark a crucial moment in the economic course of our country".
"It will be the moment that we learn that the biggest economic gamble in a generation has failed."
The Labour leader said on jobs, growth and inflation, Mr Osborne's promises had come to nothing. Growth had flatlined since the final quarter of 2010, he said, while unemployment had been growing since March 2011 while CPI inflation had been above 4% all year.
And on borrowing, he drew attention to the Office for Budget Responsibility's March prediction that £44.5bn of additional borrowing would be needed up to 2015-16 and suggested the figure was now forecast to surpass £100bn.
"When a further rise in borrowing is confirmed by the Office for Budget Responsibility next week, it will be a catastrophic blow to the government's credibility," he said.
Mr Miliband appealed to voters who backed the Conservatives at the general election, because they believed their deficit-reduction plan was right, to "look afresh at the evidence".
He said that the reason the government "no longer deserves the benefit of the doubt, is that even on this measure - the central test they set themselves - the plan isn't working".
"It isn't working because their failure to get businesses growing, to see more jobs created, has locked them and the country into a vicious cycle on the deficit," he said.
"We need to ask why, when the recovery was underway just 17 months ago, we have ended up in such a serious situation."
He said the government was wrong to blame the eurozone crisis for slow growth - it was the "scale of shrinking domestic demand" that was holding growth back.
"Austerity rhetoric" had had a "chilling effect on our economy", he said - and suggested the government was "shrugging its shoulders in the face of economic difficulty".
Those who criticised Labour's "five point plan" to boost economic growth - which would include a VAT cut and a bank bonus tax to fund youth employment programmes - for being too expensive should think again, he added.
"The cost of not acting is the more expensive choice - economically and socially. That is proved by the government missing its borrowing targets by over £100bn."
Earlier this week Prime Minister David Cameron told business leaders: "Getting debt under control is proving harder than anyone envisaged."
But he criticised Labour's plans for the economy at prime minister's questions on Wednesday, telling Mr Miliband: "Is there a single other mainstream party anywhere in Europe who thinks the answer to the debt problem is more spending and more borrowing?
"If you are worried about the level of debt, why are you proposing to add another £100bn to it? It is the height of irresponsibility and the reason why people will never trust Labour with the economy again."
Office for National Statistics figures out on Tuesday showed the UK's public sector net borrowing, excluding financial interventions, fell to £6.5bn in October - down from £7.7bn a year earlier - which the Treasury said showed Britain was making progress in cutting its deficit.