Ed Miliband claimed he will lead a "crusade to change the country" as the election campaign began in earnest with the two main parties trading blows on the state of the public finances
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 Miliband's plans for his first year in government do not add up.
But the Labour leader dismissed the Tory analysis as "completely false" and accused David Cameron of "spraying around all kinds of unfunded commitments", including £7 billion of tax cuts.
In a rally for supporters in Salford to mark the launch of Labour's election drive, Miliband 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.
He told BBC1's Breakfast: "It's a really exciting idea. Let's go and have the conversation with people, face to face, about how we want to change the country.
"It's a crusade to change the country, that's what I'm going to be part of."
Responding to the Tory attack on Labour's spending plans, he said: "It's going to be a choice between hope with us and falsehood from the Conservatives.
"The Tories are saying that they want to go back to 1930s levels of public spending as a share of our national income, that's levels of national income not seen for 80 years or so in our country.
"I don't believe you can protect the NHS with that kind of plan. It's extreme, it's ideological and I think it will be really bad and damaging for our public services."
Setting out the different approach he would take on the economy, Miliband said: "What we have had in the last five years is a country where the Tories think if you help the richest, the wealth will trickle down to everybody else.
"I've got a different way of running the country. I think: let's put working people first again in our country.
"Let's reward hard work properly, let's give opportunity to our young people. Let's take on some of those powerful interests, like the energy companies and the banks, and make them work for people."
The NHS is set to be one of the key electoral battlegrounds, and it is an issue on which Labour is confident it has an advantage over the Conservatives.
Setting out his plans for more integration between health and social care, Mr Miliband insisted that his party's proposals for a £2.5 billion annual funding boost paid for by a mansion tax, a levy on tobacco firms and a crackdown on tax dodgers would ensure the NHS is sustainable.
"It's not just a plan to hire more doctors, nurses, midwives and carers, it's also a plan to start to transform the NHS," he said.
"I do think the NHS has got to change in the future. Let me give you an example: if we hire homecare workers to keep elderly people in their own home, that's better for them and it's better for the NHS because it relieves some of that pressure of elderly people going into hospital."
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.
At the same time, he will warn that Labour's policies represent a "clear and present danger" to the economic recovery as part of his party's strategy of positioning itself as a moderating force on either of Westminster's two main powers in a future coalition.
Miliband insisted a further coalition was "best to be avoided", adding: "The way this Government has run itself, coalition government has become an excuse for each side breaking their promises, frankly."
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.