Miliband says PM must get better deal for UK in Europe
Labour leader Ed Miliband has urged David Cameron to "re-enter the negotiations" in Europe "to try to get a better deal for Britain".
He also attacked splits in the coalition over Europe during the final prime minister's questions of the year.
Mr Cameron said he made "no apologies for standing up for Britain" by vetoing changes to the EU treaty.
The exchanges came after opinion polls suggested a rise in Conservative support since the EU summit on Friday.
Sitting beside Deputy Prime Minister Nick Clegg, the PM also brushed off suggestions of a rift between them.
Mr Clegg has called the PM's decision to block EU-wide treaty change "bad for Britain".
The two men's differences on the issue were highlighted when the deputy prime minister did not attend the House of Commons on Monday for Mr Cameron's statement to MPs about using the veto in Brussels.
Mr Clegg later said his presence "would have been a distraction".
But he was present in his usual seat at PM's questions and on several occasions, whispered to - and smiled at - Mr Cameron.
The Labour leader quoted the prime minister's 2011 New Year message in which he said the coalition was demonstrating a new "more collegiate" style of politics - and asked "what's gone wrong?"
In reply, the PM made reference to Mr Miliband's relationship with his brother David, whom he beat to the Labour leadership.
"No-one in this House is going to be surprised that Conservatives and Liberal Democrats don't always agree about Europe," Mr Cameron told the Commons.
"But let me reassure him: he shouldn't believe everything he reads in the papers. It's not that bad. I mean, it's not like we're brothers or anything."
Mr Cameron also raised Mr Miliband's failure to say during Monday's session what he would have done at the EU summit, adding that most Labour MPs would be asking for a new leader for Christmas.
Despite Mr Clegg's criticism of the PM's EU decision, he told a meeting of Lib Dems MPs on Tuesday that "this government carries on until 2015, full stop".
Other European leaders had sought to rewrite the terms of the Lisbon Treaty - which governs the running of the EU - to bring about greater fiscal integration between eurozone countries.
But Mr Cameron said necessary safeguards he had sought for the UK financial services sector were not made, and therefore he could not sign up.
Mr Miliband, however, accused Mr Cameron of making "a catastrophic mistake".
He said that as the accord, being drawn up in Brussels instead of a new treaty, would not be signed until March, "isn't the sensible thing for him to do to reenter the negotiations and try to get a better deal for Britain?"
Earlier, at a meeting in London, Mr Clegg said: "As the dust settles on the summit that took place last week, I speak here on behalf of the whole coalition government, notwithstanding the differences of view between the parties within the government.
"The whole government is absolutely determined to re-engage with our European partners, to get back on the front foot and to make sure that our vital national economic self-interest in being at the heart of the single market is properly followed through the weeks and months ahead."
On Tuesday, the head of the European Commission, Jose Manual Barroso, criticised the UK's demands to protect the City of London, saying they would have disrupted the workings of the single market.
Some MEPs also called for the UK to lose its EU rebate in retaliation for its lack of "solidarity".
Mr Clegg said: "We saw some pretty intemperate remarks aimed at Britain yesterday in the European Parliament.
"I hope we can move beyond that and work together to ensure that our calm, reasoned and engaged voice is heard positively within the EU institutions in the period to come."
His Lib Dem colleague Business Secretary Vince Cable, who also attended the meeting, said: "We need to continue to work with countries in Europe because millions of jobs in Britain depend on it.
"It's complex, it's difficult, but we'd better get on with it."
Philip Souta, director of Business For New Europe, who attended the meeting, said the organisation believed Mr Cameron "did the wrong thing in using the veto".
Elsewhere, Ireland's prime minister, Enda Kenny, has said he is convinced the UK will not turn its back on the European Union.
Mr Kenny - who spoke to PM David Cameron last night - told the Irish Parliament: "What has happened is disappointing, but I would also not wish to exaggerate its import.
"The UK has decided not to participate in the specific arrangements we agreed at last week's meeting. It has not, in any way, turned its back on the European Union, as Prime Minister Cameron made clear in his speech to the House of Commons this week."
Three opinion polls published since the weekend suggest that the Conservatives have enjoyed a boost since the EU summit, which BBC Political Editor Nick Robinson said would have "real political consequences".