Ed Miliband renewed his warning to David Cameron on Thursday, that he is leading Britain towards an exit from the European Union.
The Labour leader said the prime minister's expected plan - to be set out in a keynote speech in the Netherlands tomorrow - to renegotiate the UK's relationship with the EU and then put it to a referendum would create uncertainty and damage the economy.
"The Prime Minister is taking us to the economic cliff," he told the BBC Radio 4 Today programme.
"I fear the Prime Minister's strategy is leading us towards the exit, which will cause real damage to our economy.
"If we put up a sign around Britain saying we might be out of the European Union within five years, I don't think that is going to be good for our country.
"Putting up a big flag saying 'Exit, Britain's about to get out' - is that a good negotiating strategy? I have to say that I think it is a hopeless negotiating strategy."
Mr Miliband said Mr Cameron's strategy was being driven by Eurosceptic Tories.
"He has been dragged by a neuralgic Conservative Party towards the position he is taking tomorrow," he said.
However, Mr Miliband repeatedly refused to rule out the prospect that he could seek to stage a referendum on the EU - and made clear that Labour would not repeal the Government's "referendum lock" requiring any fresh transfer of powers to Brussels to be put to a popular vote.
"There is legislation which is on the books, which we don't propose repealing, which says that if there is a transfer of powers to the European Union, then there would be a referendum," he said.
He added that he would also seek to repatriate some powers from Brussels relating to issues such as regional and industrial policy.
"I think there are areas where Britain actually needs some powers back," he said.