As the official election campaign kicks off, Ed Miliband is setting out his pitch to business leaders in a speech in the City of London.
The Labour leader said: "There could be nothing worse for our country or for our great exporting businesses than playing political games with our membership of the EU. David Cameron used to understand that. But in the past five years our place in the European Union has become less and less secure."
Mr Miliband continues: "He used to say he would campaign to keep Britain in Europe. But now he won't rule out campaigning to leave. He used to say he would be able to negotiate treaty change in Europe."
"But now he prefers to keep quiet about that too. He came to power promising to stop his party 'banging on about Europe'. Now if he carries on this way, he'll have us inside the European Union banging on the door to leave."
David Cameron has promised a referendum by 2017 if he wins the election - something that Mr Miliband described as "a recipe for two years if uncertainty."
The Labour leader added: "We'll show strong leadership to get the best for Britain, but we won't condemn this country to years of uncertainty, years of insecurity, by threatening our European future."
Lib Dem leader Nick Clegg joined in with the criticism of Mr Cameron's stance by saying he would never "play footsie " with Britain's membership of the EU.
He also warned that the country did not need a lurch to the left or the right but said the Lib Dems would keep any future government "anchored in the centre ground".
Labour's 22-page A Better Plan For Business, launched today in Bloomberg's offices, is an attempt to fight back against concerns that Mr Miliband would put the economic recovery at risk.
It is the first of a series of "mini manifestos" on key policy issues Labour will launch during the campaign.
Business insiders have told Sky News they are faced with a difficult choice between a Conservative party who would put Britain's EU membership at risk and a Labour Party that is perceived as anti-business.
David Cameron has warned that a Labour victory would cause "economic chaos."
UKIP will announce its key policies today, speaking on Good Morning Britain, Mr Farage said UKIP would not win the election but could be key in helping shape a future Government.
He said Mr Cameron had been "forced into" promising a 2017 referendum on Britain's membership of the UK and that his party's job was to "hold his feet to the fire to make sure that the referendum is not a stitch-up".
He added: "I don't want this to be kicked into the long grass until the end of 2017. I think it should be before the end of this year."
