In the run up to last week's election at the European Council meeting, David Cameron had been against the appointment of the ex-Luxembourg Prime Minister, expressing concern that his desire for a closer union would make renegotiations with the rest of Europe more difficult for Britain.
But by far the majority voted in favour of Juncker at the meeting, with only Hungary siding with the UK in what turned out to be a 26 – 2 vote.
This has left Cameron in a awkward position, since he has spent weeks openly criticising Juncker, describing him as a "career Brussels insider" and saying he was the wrong person for the position.
During a commons debate earlier today, Labour leader Ed Miliband said that Cameron has suffered "utter humiliation" as a result of the vote, and that his renegotiation strategy for the UK in Europe was now "in tatters".
But the Prime Minister said that this was not the case, accusing Miliband of being “opportunistic and wrong”.
Indeed, in parliament today Cameron said that he would work with Juncker and did not want to personalise his appointment. He also telephoned him on Sunday to personally congratulate him, and said in an article in the Telegraph that the two men had the potential for a productive relationship. "If ... we can agree that we are not heading, at different speeds, to the same place - as some have assumed up to now - then there is business we can do," he wrote.
Cameron has committed to renegotiating Britain's ties with the EU and to holding an in/out referendum in 2017, should the Conservatives be re-elected at next year's general election.
An opinion poll taken since Juncker's appointment last week has shown an increase in UK voters who say they want to leave the EU, with just 39 per cent still saying they would like to stay.