David Cameron is to tell voters they face a “stark choice” between him and Labour’s Ed Miliband as the election campaign officially gets under way.
The PM will visit the Queen for a final audience ahead of the 7 May poll, formally marking the end of the five-year coalition government.
Later, he is expected to say the UK is on the “right track” and a Labour government would be “economic chaos”.
Mr Miliband will say the Conservatives pose a clear “danger” to UK firms.
Setting out Labour’s policies on business, he is expected to warn that the PM’s promise of a referendum on Britain’s EU membership also risks an “extraordinary loss of British influence”.
After months of unofficial campaigning, the five-and-a-half week race for No 10 begins in earnest.
Parliament was formally dissolved at midnight under the terms of the Fixed Term Parliaments Act.
Analysis by political editor Nick Robinson
It’s all about you. Not them. You.
That’s worth remembering if/when you tire of all those politicians, soundbites and photo opportunities that will fill the airwaves – and your inbox – from the formal start of the campaign today, until polling day.
About you because a general election is one of those rare times when your voice counts as much as anyone else’s.
About you because you have the chance to help choose who represents you and your community in Parliament.
About you because you can influence who will run the country for the next five years and, therefore, help shape what sort of country you live in.
Rarely has there been a choice so wide or one with an impact which could be so dramatic.
Government ministers remain in charge of their departments until a new administration is formed but MPs will cease to be members of Parliament and writs will be issued for elections in all 650 constituencies.
Issues likely to dominate the campaign include the economy and spending cuts, Britain’s EU membership and immigration.
After meeting the Queen at Buckingham Palace, Mr Cameron is expected to make a statement outside Downing Street in the afternoon.
It is understood he will say that “after five years of effort and sacrifice… this election is about moving forward”.
Policy guide: Key priorities
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Mr Cameron will say the “next prime minister walking through that door will be me or Ed Miliband” and a Conservative government would oversee “an economy that grows, that creates jobs, that generates the money to ensure a properly funded and improving NHS”.
He will say Labour leader Mr Miliband “pays lip service to working people while planning to hike taxes and increase debt”.
But in a speech later setting out Labour’s “business manifesto”, Mr Miliband will say the Tories represent a “clear and present danger” to jobs and prosperity by risking an exit from Europe.
Setting out Labour’s commitment to UK membership of the EU, he will also promise to “return Britain to a leadership role” in Brussels.
Labour has said the economic recovery under the coalition has been the slowest in more than 100 years and resulted in a cost-of-living crisis.
It has pledged to raise living standards of “everyday working people by ensuring those with the broadest shoulders bear the greatest burden” while cutting the deficit and securing the future of the NHS.
Elsewhere, Deputy Prime Minister and Lib Dem leader Nick Clegg will have a separate private audience with the Queen on Monday in his capacity as Lord President of the Privy Council.
Campaigning in Oxfordshire on Sunday, Mr Clegg said leaving the EU would be an act of “self-harm” and risked the UK’s economic recovery.
It came as one of his senior colleagues, Energy Secretary Ed Davey, suggested the Conservative’s commitment to an in-out EU referendum would make a second coalition with them “incredibly difficult”.
Both David Cameron and Ed Miliband have conceded the election is on a “knife edge” with opinion polls suggesting there is little to split the Conservatives and Labour.
A ComRes survey for ITV News and The Daily Mail on Monday suggested the Conservatives were leading Labour by 36% to 32% but a YouGov poll for the Sunday Times suggested the reverse, putting Labour on 36% and the Tories on 32% nationally.