International Monetary Fund chief Christine Lagarde has ruled herself out of the race to be president of the European Commission, insisting: "I am not a candidate."
The possibility of Ms Lagarde taking the EU's top job had reportedly been discussed by German chancellor Angela Merkel and French president Francois Hollande after David Cameron made clear Britain's implacable opposition to the front-runner, Jean-Claude Juncker.
Shortly before joining Ms Lagarde at a press conference in London today, Chancellor George Osborne underlined Britain's insistence that the new Commission president must be someone who understands "the need for change" in the EU.
Mr Juncker, a former prime minister of Luxembourg who is regarded in London as an arch-federalist opponent of reform, has apparently spoken out privately against the UK's efforts to block his candidacy.
According to the Guardian, Mr Juncker, who insisted earlier this week he is "more confident than ever" of landing the job, told allies in the centre-right EPP grouping in the European Parliament: "It is wrong if we give in to the British here. I will not be forced to get on my knees before the British."
Asked at the IMF press conference at the Treasury if she would consider leading the Commission after current president Jose Manuel Barroso steps down in October, Ms Lagarde said she intended to see out her five-year term as managing director of the world financial watchdog, which ends in 2016.
"On this EU thing, I am not a candidate," said the former French finance minister. "I have a job, I happen to think it is a rather important job and I intend to complete my term."
Mr Cameron has made no secret of his vehement opposition to Mr Juncker's candidacy and is said to have warned European leaders last week that Britain could leave the EU if the arch-federalist succeeded. He and Mrs Merkel held talks over the issue on the fringes of this week's G7 summit in Brussels in an attempt to find a way forward.
Mrs Merkel has publicly backed Mr Juncker to succeed Mr Barroso, but unconfirmed reports earlier this week suggested she had privately raised with Mr Hollande the possibility that he might put Lagarde's name forward.
Mr Osborne declined to discuss individual candidates for the presidency, insisting that the Government's priority was ensuring that the new Commission was committed to reform. The UK has not yet given public backing to any candidate.
The Chancellor told BBC Radio 4's Today programme: "Our view - David Cameron's view, my view and everyone else's in the Government - is that we need people running these European institutions who clearly understand the need for change.
"We've just had European elections where not just in this country but across Europe people said very clearly they weren't happy with the way Europe is working.
"Anyone who wants one of these important jobs in Europe, which affect all of our lives, needs to demonstrate, in my view, that they understand people's anger at what's gone wrong in Europe, understand the need for change in Europe.
"It's for anyone who is aspiring to one of these important jobs in Europe to set out their case. That's the test we are going to apply as a British Government."
Asked whether the UK risked antagonising the man who may be at the helm of the European Commission over the next five years, Mr Osborne said: "Everyone aspiring to this job... understands that Britain is seeking change for Europe's sake, not just for Britain's sake, so we create more jobs and prosperity across the continent.
"There is a stark contrast at the moment between Britain's economic performance and the very weak economic news we receive from too many of our European neighbours. That's not good for us and it's certainly not good for them.
"We've got to have a response across Europe to the election results, to the weak economic performance. We've got to have change in Europe and that is what the Conservative Party is promising and the referendum we offer - unlike any other party - will be something that people can look at at the general election."
Mr Juncker was also reported to have complained about coverage of his candidacy in the British press.
"What bothers me is the gathering British press campaign," he is reported to have said. "The tabloid press has occupied my house, photographers are harassing my neighbours, they are asking neighbours about family stories.
"You had better be ready for a lot more dirt."
Austrian MEP Othmar Karas - a vice president of the European Parliament whose People's Party is a member of the EPP - said the UK blocking Mr Juncker's appointment would be a "flagrant disrespect for democracy".
He said the politician was exactly the sort of "consensus builder" that the EU required.
"We need leaders who can bridge differences. He is the right one to do it," he told BBC Radio 4's The World At One.
"The fact that the European party the Tories belong to did not nominate any top candidate is not the fault of the other parties.
"Not making Juncker president would be a flagrant disrespect for democracy and for smaller countries in the European Union.
"One country cannot impose its will."
He went on: "We don't need the vote of David Cameron, we don't need an unlimited majority in the council."