David Cameron returned from the European Council as a failure and suffering "utter humiliation" after Jean-Claude Juncker was nominated to be the new Commission president, Ed Miliband claimed today.
The Labour leader tore into the Prime Minister after Mr Cameron reported to MPs on the summit, which saw European leaders vote 26-2 in favour of Mr Juncker.
Mr Cameron insisted his actions represented standing by a point of principle and had made it clear Britain would not back down on issues of importance.
But Mr Miliband said: " You returned to Britain on Friday having failed. Not some mild small failure, but an appalling failure of relationship building, winning support and delivering for Britain.
"I know it is inconvenient to remind you, but you lost by 26 votes to two. And then you come to this chamber and seem to claim it as a complete vindication of your tactics.
"Your party may think it represents splendid isolation - it isn't. It is utter humiliation."
In his statement, Mr Cameron said he did not agree with the European Parliament effectively choosing the new president of the commission, believing this was a power which should be retained by national government leaders in the council.
"I firmly believe it should be for the European Council, the elected heads of national government, to propose the president of the European Commission," the Prime Minister told MPs.
"It should not be for the European Parliament to try and dictate that choice to the council. This is a point of principle on which I was not prepared to budge.
"In taking this position, I welcomed the support of the Leader of the Opposition (Mr Miliband) as well as the Deputy Prime Minister (Nick Clegg) in opposing the imposition of Jean-Claude Juncker.
"I believe the council could have found a candidate who commanded the support of every member state - that has been the practice on every previous occasion and I think it was a mistake to abandon this approach this time."
Mr Cameron said Labour had given away the veto on who was commission president by signing the Nice and Lisbon treaties.
But he told MPs: "Once it was clear the council was determined to proceed, I insisted the European Council took a formal vote, something which doesn't usually happen.
"Facing the prospect of being outvoted, some might have swallowed their misgivings and gone with the flow but I believe it was important to push the principle and our deep misgivings about this issue right to the end.
"I at least wanted to put Britain's opposition to this decision firmly on the record."
Mr Cameron said it was a "bad day for Europe" which risked undermining national governments and parliaments.
But he welcomed the decision to review the process the next time the position becomes vacant.
Looking to the future, Mr Cameron said: "We must work with the new commission president as we always do to secure our national interest.
"I spoke to him last night and he repeated... his commitment in his manifesto addresses British concerns about the EU."
The Premier said the issue had underlined his convictions that "Europe needs to change".
And Mr Cameron pointed to "modest progress" in arguing for reform at the council, highlighting agreements to focus on the economy and freedom of movement.
He said: "So while Europe has taken a big step backwards in respect of the nomination of the Commission President, we did secure some small steps forward for Britain in its relationship with the EU."
But he warned: "Last week's outcome will make renegotiation of Britain's relationship with Europe harder and it certainly makes the stakes higher - there will always be huge challenges in this long campaign to reform the European Union but with determination, I believe we can deliver."
The anti-Juncker movement had a "toxic supporter" in Mr Cameron, who other European leaders believe is trying to pacify Eurosceptic Tories rather than solve the problems in the EU, Mr Miliband said.
The Prime Minister's failure to get support from other EU leaders showed his strategy of renegotiating Britain's relationship with the EU is "in tatters", he added.
The Labour leader derided Mr Cameron's strategy of using "threats, insults and disengagement" as "a masterclass in how to alienate your allies and lose the argument for Britain".
Mr Miliband claimed Mr Cameron's actions over the last four years - in leaving the EPP centre-right coalition of European parties, and "throwing his hand" in with the German equivalent of Ukip - meant he had lost backing from crucial allies such as German chancellor Angela Merkel.
Claiming the PM favoured "short-term party management" over acting in Britain's national interest, the Opposition leader said: "The problem for the anti-Juncker cause is it had a toxic supporter - you.
"And isn't the reality that you could not attract any allies because the rest of Europe simply lost patience as a result of your actions, not just in the last few weeks but in the last few years?
"It comes down to this - when you come calling they believe you are doing so to help solve the problems of the Conservative Party, not the problems of the European Union."
Mocking Mr Cameron's meeting with the German, Dutch and Swedish leaders on a boat in Sweden, and pointing out they all voted for Mr Juncker, Mr Miliband went on: "You couldn't get four countries to support you over Mr Juncker and if you can't get four countries to block the appointment of a president, how on earth are you going to get 27 countries to support a new treaty?
"This weekend has shown conclusively to everyone but you - your renegotiation strategy is in tatters.
"We know where it will end - you will be caught in the gulf between your backbenchers who want to leave and what you can negotiate.
"You failed over Mr Juncker, you were outwitted, outmanoeuvred and outvoted. Instead of building our alliances in Europe, you are burning them.
"You are a defeated Prime Minister who cannot deliver for Britain."
Responding, Mr Cameron said Mr Miliband's claims were "weak, opportunistic and wrong", and likened him to former Labour leader Neil Kinnock, to the delight of Tory backbenchers who roared their support.
The Prime Minister said Mr Miliband was not even invited to the meeting of centre-left European leaders in Paris, all of whom backed Mr Juncker, showing he had little influence in the EU.
Mr Cameron said: "Well we've had yet another performance worthy of Neil Kinnock.
"Endless words, endless wind, endless rhetoric - no questions, no grit, and no ability to stand up for Britain.
"I have to say I won't take lectures on negotiation from the people who gave away the veto, who gave away the rebate, who backed down on the budget every year, and who even signed us up to euro bailouts.
"We won't take any lectures from you."
He went on: "You talk about the ability to get together allies, where were your allies in the socialist party?
"They had a meeting in Paris - all the key socialist leaders were there, they all decided to support Jean-Claude Juncker. Where were you? Not even invited. That's how much influence you've got."
Mr Cameron added: "I have to say - to support the Government over opposing this principle and opposing this individual only to criticise and complain is typical of your approach - weak, opportunistic, and wrong."