The Conservative and Liberal Democrat parties have both attacked the Labour manifesto.
Prime minister Gordon Brown chose a newly-built hospital in Birmingham to lay out his pitch to the voters earlier today.
Shadow defence secretary Liam Fox said the manifesto suffers from "a distinct lack of ambition and imagination".
Lib Dem leader Nick Clegg accused Labour of promising to make the UK a more fair country in previous manifestos.
"They are doing it again," he said.
"If they haven't managed to do it in 13 years, why would anyone believe they are going to do it this time?"
Before this morning's launch the Conservatives released a document analysing the Labour party's 2005 manifesto.
"They have broken no fewer than 102 promises," according to the Tory party website.
"We've had thirteen years of Labour's broken promises and nothing changes.
"What Britain needs is change – and only the Conservative party has the energy, leadership and values to bring about that change."
Tory leader David Cameron accused the government of "a very negative campaign, all about attack and trying to scare people".
The Conservatives are due to publish their manifesto on Tuesday and the Lib Dems on Wednesday.
Today Clegg and Lib Dem Treasury spokesman Vince Cable unveiled plans to raise the income tax threshold to £10,000, lifting more than three million people out of income tax.
