Britain is "sleepwalking" towards an exit from the European Union because of growing euroscepticism in the Conservative party, Ed Miliband has warned.
The Labour leader used an interview with the Sunday Telegraph to express his fears about the impact such a move could have on Britain's economy, ahead of his address to business leaders at the CBI annual conference tomorrow.
"I think it's clear the way the centre of gravity of the Conservative party has moved, and I think that is quite dangerous for the country and I think quite dangerous for business above all," he said.
Miliband allied with Tory eurosceptics to defeat the prime minister in a Commons vote on the EU budget earlier this month. That has limited Cameron's negotiating ability in this week's Brussels summit as he seeks a real-terms freeze to the EU budget.
Divisions within the government were emphasised by Miliband, however, who pointed out that education secretary Michael Gove has suggested he would vote for a withdrawal from the EU if a referendum took place tomorrow.
The Labour leader asked: "What's happened to collective responsibility? It's partly probably jockeying for a post-Cameron world but I think the business community is genuinely very worried.
"I think they are genuinely worried that we're going to sleepwalk towards an exit under Cameron."
Cameron has already conceded he is open to the idea of a referendum on Britain's continuing membership of the EU, but is insisting the move does not take place until the eurozone crisis has been resolved.
Miliband, whose party remains broadly in favour of Europe, has responded to growing frustration with the continent by targeting his own political anger at the EU budget.
"Too often people have assumed that we have got to make the rise of euroscepticism about the mythology of bendy bananas and bans on chocolate, not the fact that the European budget looks like it's suited to the 1950s and not the 21st century," he added.
"What I would say is - never shrink from being open about the problems of the European Union."
Even Liberal Democrat business secretary Vince Cable, another pro-European, acknowledged that the eurozone crisis has changed the terms of Britain's engagement with the EU.
"I think to the extent to which there's rethinking, we do need to focus our attention on markets outside the European Union," he told BBC1's The Andrew Marr Show.
He rejected calls for a withdrawal from some of his Cabinet colleagues, however, adding: "It's potentially very damaging to suggest rethinking in a fundamental way our relationship with the European Union."