British Prime Minister David Cameron called Jean-Claude Juncker on Sunday to congratulate the man he tried to block from becoming European Commission president, Downing Street said in a statement.
Cameron's failure to prevent Juncker getting the job after a bitter campaign was seen as a blow to the premier that could increase the likelihood of Britain leaving the European Union.
A spokesman for the prime minister said Cameron had phoned to congratulate Juncker on his successful campaign, and on securing the nomination.
"They discussed how they would work together to make the EU more competitive and more flexible," the spokesman said.
"The PM welcomed Mr Juncker's commitment of finding a fair deal for Britain and Mr Juncker said that he was fully committed to finding solutions for the political concerns of the UK."
Juncker, a former Luxembourg prime minister, was nominated to take the EU's top job on Friday.
A veteran Brussels insider, Juncker was supported by all EU members except for Hungary and Britain, where eurosceptic sentiment has been increasing.
Cameron had initially described Juncker's victory as "a bad day for Europe" that risked undermining the power of national governments.
The British prime minister's failure to block Juncker was seen as likely to increase support in Britain for an exit from the EU, with Cameron commenting that the task of keeping Britain within the bloc had got harder.
Britain is due to hold a referendum on membership of the 27-country bloc if Cameron's Conservative party wins a general election next year.
In the meantime, Cameron has vowed to push for changes in Europe, such as bringing some of its powers back to Britain.
The spokesman said Cameron and Juncker would speak further at a European Council meeting on 16 July -- where the heads of government are due to discuss candidates for a range of senior EU jobs.