Gordon Brown today warned that a Tory government would put Britain's "fragile" recovery at risk.
The Prime Minister told a London news conference David Cameron's "big society means big cuts in public services.
"It's a risk for our mainstream public services that Britain cannot afford to take."
Mr Brown was attempting to shift the election spotlight away from Liberal Democrat leader Nick Clegg's recent poll successes and back on the substantive issues like the economy.
He said Labour was in the "futures business" with bold and ambitious plans for the country, while the Tories were in the "risk business".
Mr Brown's warning came as Labour launched a spoof newspaper front page and radio news broadcast warning of "an emergency Budget backlash" if the Tories took power.
Business Secretary Lord Mandelson said that, if Mr Cameron got the keys to Number 10 Downing Street, George Osborne, as Tory Chancellor, would deliver an emergency Budget in June.
According to the broadcast, Britain would be struggling to contain its anger after Mr Osborne had been "forced to make significant reductions" in public services and leading economists had warned that a "double-dip recession" was a real possibility.
Mr Brown said last week's campaign has been "a tale of two Nicks" - focusing on National Insurance contributions (Nics) and Nick Clegg.
But this week the parties would be focusing on the "big questions about our country's future."
He said economic indicators showed the country continued to emerge from recession but "the recovery is fragile" and it was not a time to put that at risk with a Conservative government.
Chancellor Alistair Darling accused the Tories of not spelling out the consequences of cutting £6 billion from public spending and accused Mr Osborne of being "reckless" with the economy.
Mr Darling maintained that Labour had supported efforts to reduce job losses during the recession and taken moves to stop families losing their homes.
He told the press conference he was optimistic about the future of the economy, but added: "We are not yet out of the woods and now is not the time to be making cuts."
Mr Darling claimed that, under the Tory plans, 14,200 teachers could lose their jobs and there could be 2,400 fewer police as part of the public spending cuts.
"I am optimistic about Britain's economic future and I am confident we will see a return to strong growth next year."
He accused Mr Osborne of "compounding" the problems a future government would have to face, adding: "Were George Osborne to be elected, he has compounded these problems time and again by taking a reckless approach to public finances, presenting this country with a huge risk."
Labour today published what it described as the Tories' emergency Budget, giving details of where it believed cuts would have to made.
The party issued a document warning that the economic recovery would be put at risk, teachers and police numbers would be cut and families on modest incomes would lose Child Tax Credits and the Child Trust Fund.
Asked about the Goldman Sachs investigation, Mr Brown said: "If people knew they were deliberately selling products that were worthless, or likely to be worthless, that is a breach of any of the codes of trust that banking should uphold.
"This practice cannot be allowed to continue."
The Government was "determined to root it out".
Mr Brown said the Conservatives' economic policies would do "enormous damage to the economy and make sure the recovery was put at risk by taking money out of the economy now.
"That is simply a risk too far."
The Prime Minister said the election was now "wide open" with debate getting under way on the "big issues".
He said: "Some of the Liberal policies I don't find very attractive. Child Tax Credits have helped half a million people through the recession. The Liberals want to cut them. That is a mistake."
Mr Brown said he was making progress in talks with France, Germany and the United States on a global financial levy but warned against acting unilaterally.
"You don't want a race to the bottom in banking," he warned.
Questioned about the increased popularity of Mr Clegg following last week's debate, Mr Brown said: "I know a little about what it means to have a short political honeymoon. You go through these phases. I wish him well in his."
But the Prime Minister continued to distance himself from Lib Dem policies, especially Mr Clegg's strong call for the Trident nuclear submarine system to be scrapped.
"Are we going to give up our nuclear weapon at a time when Iran is trying to acquire one?
"I am not in favour of unilateral action when North Korea and Iran are getting nuclear weapons.
"We would look as if we were putting ourselves at risk. Unilateral action is a mistake."
Mr Brown said Labour did not support the Lib Dem position on tax credits, although he maintained that Mr Clegg's party would support Labour on raising the top rate of tax.
Asked about the next leaders' debate on Thursday, Mr Brown said the future discussions for the rest of the election campaign would be on big issues such as the future of the economy and public services.
And the Prime Minister said of David Cameron's policies: "His vision is of DIY, you're-on-your-own public services."
* One of the people reading spoof items on Labour's news "bulletin" was Alastair Campbell, the party's former communications chief.Reuse content