Both sides accused the other of betraying a large proportion of the population in a row over plans for a real terms cut in benefits.
It followed a move by Nick Clegg suggesting Labour would have to cut money for schools and hospitals to pay for higher benefits increases.
The Deputy Prime Minister contrasted Labour's opposition to the 1% benefits cap, far below inflation, with support for a 1% pay rise in the public sector.
Labour, meanwhile, accused the Coalition of pushing millions of the working poor into poverty.
Earlier, the Coalition released statistics suggesting benefits have risen almost twice as fast as wages in recent years.
But Labour produced its own analysis suggesting Jobseeker's Allowance had risen by less than earnings over the past decade.
Legislation to bring in a 1% cap, and break the traditional link between benefits rises and inflation, will be debated by MPs for the first time on Tuesday.
The cap, well below the expected rise in the cost of living, will last three years and apply to many working-age benefits and tax credits from this year.
Child benefit, housing benefit and Universal Credit will also be capped for two years from 2014/15 in moves predicted to save the Government £2.4 billion by the 2015 General Election.
But the Tories claim Labour has walked into their "elephant trap".
They say the polling shows voters are fed up with what they see as the so-called "shirkers" in society.
But Labour insist the Coalition has it wrong and the public will accuse them of heartlessness.
Tory chairman Grant Shapps insisted his party was on the side of fairness.
"It's difficult to justify when the public sector, for example, are being kept to a 1% pay rise, that benefits should increase faster, than say your average public sector worker."
Echoing Mr Clegg's comments, he said Labour has to explain how it would pay for benefit payment increases.
Labour has refused to set out its tax and spending commitments, saying that unlike Mr Clegg it would not "make promises we cannot keep".
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