Cameron mends ties with Juncker

"They discussed how they would work together to make the EU more competitive and more flexible. The prime minister welcomed Juncker's commitment of finding a fair deal for Britain, and Juncker said that he was fully committed to finding solutions for the political concerns of the UK," a spokeswoman for Cameron told press in London.

Cameron needs to mend ties with Juncker in order to secure a decent EU commissioner portfolio, as member states have now begun the horsetrading for key posts in the new EU commission.

Some EU diplomats already quip that UK will get "multilingualism" – a portfolio created in 2007 for Romania after it failed to send a proper candidate in the first run.

The UK leader has come under criticism at home for his attempts to block Juncker during last week's EU summit where he triggered an unprecedented vote but failed to gather the required blocking minority.

"I think this weekend was a catastrophe for Britain and the British national interest. I've never seen a negotiation so cack-handed," opposition Labour MP Ed Balls said Sunday on BBC.

With British MPs on Monday to grill him on the matter, Cameron wrote in the Telegraph that he strongly believed that the "important principle" of not letting the European Parliament "dictate" who to choose as commission president was at stake.

"It was important to stand up for it – even if it meant being isolated, because sometimes it is possible to be isolated and to be right," Cameron wrote.

"Of course, the result did not go our way. Jean-Claude Juncker has been nominated as the next president of the European commission, and we will now work with him," he added.

Cameron said he "inherited" the voting system – by qualified majority – from the previous government and rejected criticism that he failed to gather enough allies for a veto. Only Hungary voted against Juncker alongside Britain.

He also said it would be a "wrong conclusion" to say that this is a "fatal blow" to his attempts to renegotiate Britain's terms of EU membership before putting it to a referendum.

"I do not deny that it has made the task harder and the stakes higher. But it is not in our nature as a country to give up," Cameron wrote.

A weekend poll published by the Mail on Sunday showed that 47 percent of Britons want to leave the EU, while 39 percent want to remain in the bloc.

Meanwhile, German finance minister Wolfgang Schaeuble told the Financial Times on Sunday that Berlin would do everything it can to keep the UK in the EU.

"The EU without the UK is absolutely not acceptable, unimaginable. Therefore we have to do everything so that the interests and the positions of the UK find themselves sufficiently in European politics," Schaeuble said.

Germany was key in Cameron's miscalculation of the Juncker nomination. Chancellor Merkel was first hesitant about the Luxembourg politician, but then outright backed him when domestic public opinion turned against her.