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, marking the end of the five-year coalition government, ahead of the 7 May poll.
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 and present danger" to UK firms by risking an exit from Europe.
After months of unofficial campaigning, the five-and-a-half week race for No 10 begins in earnest.
Parliament has been formally dissolved under the terms of the Fixed Term Parliaments Act.
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.
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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".
He 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".
Parliament is officially dissolved under the terms of the Fixed Term Parliaments Act But setting out Labour's policies on business on Monday, Mr Miliband is expected to warn that the Tory promise of a referendum on Britain's EU membership poses a "clear and present danger" to jobs and prosperity.
It also risks an "extraordinary loss of British influence", he will say, as he promises to "return Britain to a leadership role" in Brussels under Labour.
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.