David Cameron has warned fellow EU leaders of "consequences" if they press ahead with plans to nominate an arch-federalist, whom Britain regards as an obstacle to reform, as president of the European Commission.
The Prime Minister insisted he was "completely unapologetic" about his outspoken opposition to the appointment of former Luxembourg premier Jean-Claude Juncker, which has left him isolated at a two-day summit of the European Council.
Mr Juncker's nomination to the EU's top job is expected to be confirmed in an unprecedented vote in Brussels tomorrow, breaking a decades-old tradition that the Commission chief is chosen by consensus of the EU's national heads of government.
But Britain insists that its dissatisfaction with Mr Juncker is "not a unique view" and that privately other capitals have misgivings about his candidacy.
Amid widespread reports that Mr Juncker's liking for "a cognac at breakfast" were causing concerns in Brussels, one European diplomat said : "His alcohol consumption has been raised by a number of leaders since the (European) parliamentary elections."
With Chancellor Angela Merkel throwing Germany's weight behind Mr Juncker - despite reportedly assuring Mr Cameron initially in private that he would not get the job - and other potential allies such as Sweden and Netherlands also dropping their opposition, only Hungary remained as a possible partner for Britain in voting against his installation.
But Mr Cameron said he continued to believe his fellow leaders were making a "mistake" and that choosing Mr Juncker - candidate of the largest political grouping in the European Parliament, the centre-right EPP - would be "bad for all of Europe".
In an apparent swipe at leaders who have voiced disquiet behind closed doors, Mr Cameron said: "It's very important in Europe that you say what you say in private and it's the same as what you say in public."
Asked whether there could be consequences if the other 27 leaders refuse to accept the need for consensus, the Prime Minister said: "Everything has consequences in life.
"Obviously, I think proceeding in the way that countries are planning to proceed in choosing this individual, I believe that this is the wrong approach. And I think that would be bad for... all of Europe."
Mr Cameron made clear that defeat in Brussels would not affect his determination to press ahead with renegotiation of Britain's EU membership, followed by an in/out referendum in 2017, if Conservatives win next year's general election.
"Does any of this mean that we do not get a renegotiation? No," he said. "Does it mean we don't get a referendum? No."
But it is understood that the Prime Minister believes that a refusal on the part of the European Council to take account of the reservations of a large member of the EU - and a net contributor to its budget - will have an impact on the mood in which the referendum debate is conducted in the UK.
One British official said: "We are realistic that that has an impact on the debate in Britain about the EU. That's what other leaders must realise... What we have been saying to people is 'You need to realise that there is a debate going on in Britain about Britain's role in the EU. It's not one prime minister, leading one party, with a view. There is a broad debate here, and you need to understand that political reality'."
Victory for Mr Juncker would "make securing reform and securing renegotiation even more important and will make us even more determined", said the official.
Mrs Merkel appeared to offer an olive branch to Mr Cameron as she arrived for talks with fellow centre-right leaders ahead of the summit, saying that there was room for a "good compromise for the UK" in a document setting out the EU's strategic agenda for the next five years.
This consolation prize could involve strong words in the document - due to be signed in Brussels tomorrow - on British prioritiessuch as jobs, growth, deregulation, immigration and "welfare tourism", which might act as a constraint on the actions of an eventual Juncker Commission.
British officials were playing down speculation that agreement on the Commission presidency might be reached through horse-trading over other top jobs - including the offices of European Council president and High Representative for foreign affairs, which also come up for renewal in November - insisting that Mr Cameron will make good on his promise to maintain his opposition "until the end".
Britain is angling for one of the key economic portfolios at Berlaymont, but decisions on individual commissioners are not expected until a later summit next month.
The prime ministers and presidents of the 28 EU states set aside their differences on the first day of the summit to commemorate the 100th anniversary of the outbreak of the First World War in a ceremony at Ypres, scene of some of the conflict's bloodiest battles.
After a minute's silence at the Menin Gate - where the name of one of his great-great-uncles is inscribed among the war dead - Mr Cameron told the other leaders at dinner that the event reminded him of the central role Britain played in Europe's past and said that he was committed to ensuring it played a central role in its future.
In a reminder of his call for the goal of "ever closer union" to be scrapped, he stressed the need to respect the role of nation states within the EU and to recognise that not all of them are heading towards the same destination.
Labour accused Mr Cameron of mishandling the issue by "playing the man, not the ball".
Shadow foreign secretary Douglas Alexander told the BBC: "Sadly, the handling of these negotiations have turned a Europe divided over Jean-Claude Juncker into a Europe apparently united against David Cameron.
" What we needed was to work to build an alliance with countries that were themselves unconvinced by Jean-Claude Juncker's candidacy - countries like Sweden, Denmark, Holland, Hungary, Italy. There was an alliance there to be built, but alas it appears that the Prime Minister so badly misjudged his tactics and strategy that that is not going to be the outcome in the next 24 hours."