Talking to the Today programme's James Naughtie, the Labour leader, Ed Miliband, has said the prime minister's stance on Europe is taking Britain to the "edge of an economic cliff".
David Cameron is expected to use a speech tomorrow to argue for a referendum on future changes to the UK's relationship with the EU.
Mr Miliband has refused to rule out such a vote in the future and admits there are areas for negotiation but he has accused the government of taking the wrong stance now: "I don't think the contested ground in this... is the need for change, the contested ground is how do we change it."
"Putting up a big flag saying exit, Britain's about to get out, is... a hopeless negotiating strategy because I think the idea that people are more likely to accede to you demands if you say well actually we're just going to walk away and Britain can sort of be written off, I honestly don't think that's going to help us."
Ed Miliband said he wanted a "flexible Europe" where areas of policy could be negotiated.
"I think there are areas where Britain needs some powers back," he said and sited regional and industrial policy as examples of these.
In a reaction to the think-tank, Migration Watch's warning that about 50,000 people will come to Britain from Romania and Bulgaria, when EU restrictions are lifted on these countries next year, Mr Miliband, said his party "didn't get it right on immigration in the past" and he supported moves to try to limit the numbers of immigrants.
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