George Osborne will lead senior Tories in an attack on Labour's general election promises, accusing the party of pledging £20.7 billion in unfunded spending commitments.
The Chancellor, flanked by four Cabinet colleagues, will use Treasury costings to claim Ed Miliband's plans for his first year in government do not add up.
The Labour leader, meanwhile, will set out his pitch to voters and urge party activists to get out on to the doorstep in a "street by street" campaign to regain power at the general election in May.
In a rally for supporters to mark the launch of Labour's election drive, he will call on them to hold four million individual conversations with voters - almost double the number achieved at the last election in 2010 - setting out their case in the run-up to polling day.
Deputy Prime Minister Nick Clegg will use his first press conference of the year to brand Tory plans to tackle the deficit "a con" as he continues to attempt to distance the Liberal Democrats from their coalition colleagues.
The series of events as MPs return to Westminster after the Christmas recess marks the ramping up of campaigning ahead of the May general election.
Chris Leslie, shadow chief secretary to the Treasury, said: "It is David Cameron and George Osborne who have made over £7 billion of unfunded tax promises. These could only be paid for by another Tory VAT rise, even deeper cuts to public services or both.
"Labour has made no unfunded commitments. In fact the Institute for Fiscal Studies said last month that we had the most cautious approach and, unlike the other parties, had promised no net giveaways.
"If the Tories wanted a serious debate they would not be blocking our proposal to allow the OBR to independently audit the manifestos of the main parties. Instead it's clear they want to carry on spreading smears about Labour while avoiding scrutiny of their own plans.
"It is George Osborne's plan to slash public spending back to a share of national income last seen in the 1930s which is the real risk to Britain's future."
Mr Miliband's promise of a grassroots campaign comes after the party's chief election strategist, Douglas Alexander, claimed last week that the Conservatives could outspend them by three to one in the battle for No 10.
Speaking in Greater Manchester, the Labour leader will tell activists that they face "a once-in-a-generation fight" to determine who the country really works for.
"It is a choice between a Tory plan where only a few at the top can succeed and our public services are threatened - or a Labour plan that puts working people first, deals with the deficit and protects our NHS," he is expected to say.
"We will offer hope, not falsehood. We know the depths of our values matter more than the depth of our opponents' pockets. We will win this election, not by buying up thousands of poster sites, but by having millions of conversations.
"This year we will be making our case, explaining our vision, house by house, street by street, town by town."
He will launch a renewed attack on the Conservatives' record in office, accusing them of stripping back government to the "bare bones" while handing tax cuts to the wealthy, leaving working people worse off and damaging the NHS.
"David Cameron said he would eliminate the deficit by 2015. Well, 2015 is now here - and so is the deficit," he will say.
"It is still here for a very simple reason: because it turns out if you depress wages and lack any real economic plan other than tax cuts for the wealthy, it doesn't just fail working people, it fails to balance the books.
"So this Tory experiment has been tried. And the verdict is in: the Tory experiment has failed. Theirs is not a record to run on. Theirs is a record to run from."