David Cameron's failure to block the appointment of Jean-Claude Juncker to the European Union's top job shows he poses a "real and present danger" to the British economy, Ed Miliband has claimed.
The Labour leader said the "debacle" over the arch-federalist's nomination had taken the UK closer to the "exit door" that could put three million jobs and tens of thousands of businesses at risk.
Health Secretary Jeremy Hunt accused EU leaders of "cowardice" for backing the former Luxembourg premier as the next president of the European Commission and insisted British voters would be "proud" of the Prime Minister.
But, w riting for the S unday Times, Mr Miliband claimed that Mr Cameron had demonstrated that he "is incapable of reforming Europe".
" The lesson of the Juncker debacle is that David Cameron and the Conservative Party now pose a real and present danger to our economy," he wrote.
" He could not build alliances and his threats succeeded only in turning a Europe that was divided over the best candidate for commission president into a Europe united against him.
"There can be no better indicator of how a Conservative government would damage Britain's national interest and Britain's businesses if it were to win a second term next year.
"Mr Cameron blusters about bullying 27 other member states into agreeing fundamental treaty change before a referendum on withdrawal. But the isolation he achieved this week is not 'splendid'. It shows he is incapable of reforming Europe and his strategy of getting change by making threats to leave to get change does not work.
"All it does is take Britain closer to an exit door through which three million British jobs and tens of thousands of businesses could disappear.
"By contrast, it is a Labour government that would win the argument and build alliances for the reform that is much-needed and entirely possible: a budget and institutions that support jobs and growth, rules on immigration and benefits that recognise the needs for change and greater powers for national parliaments."
Mr H unt attacked EU premiers for saying they would oppose the arch-federalist's nomination in private only to then support him publicly.
He said: "As a result of cowardice yesterday from other leaders who weren't prepared to stand up in public and say the things they had said in private, they're going to have to work a lot harder to persuade the British people that Europe can be trusted with a proper reform agenda that's going to make it strong and competitive in a very tough global economy."
After the defeat Mr Cameron conceded that he faces a tougher fight to persuade Britons to vote to remain in the EU.
But Nigel Farage said the drubbing showed Mr Cameron would not be able to renegotiate Britain's relationship with Brussels and claimed EU leaders would rather see the UK leave than thrash out a substantial new deal.
He told BBC Radio 4's Today programme: "In terms of the fundamental changes that the British people really want in this relationship, namely we want a trade deal and not membership of a political union, I would say this to you: the other European leaders and certainly the European Parliament would rather the United Kingdom left the EU than start to pick apart the treaties because if they do that they know there'll be half a dozen other northern European countries that will demand the same."
Sweden's prime minister Fredrik Reinfeldt said he was willing to "walk the extra mile" to address British concerns over the EU.
He said the strategic agenda agreement took into account UK concerns over an ever closer union.
"Just look into what we have written in our conclusions," he told Today.
"You will find references with text, which I think is very important for David Cameron, saying this ever-closer union perception is maybe not the best for everyone."