Suggestions that David Cameron has left Britain isolated in Europe by deploying his veto were downplayed today by German Chancellor Angela Merkel, who insisted the UK will continue to play an important role in the EU.
Mr Cameron told the House of Commons he would "make no apology for standing up for Britain" by blocking treaty changes to shore up the eurozone, forcing the other EU members to strike their own "fiscal compact" outside the official treaty framework.
But he was accused of making a "catastrophic mistake" by Labour leader Ed Miliband, who urged him to re-enter negotiations with the other 26 EU states to try to get a better deal for Britain.
The clash came in the final session of Prime Minister's Questions before Christmas, at which Mr Cameron was flanked on the Government frontbench by his Liberal Democrat deputy Nick Clegg, who has described the failure to get a deal at last week's European Council summit as "bad for Britain".
After staying away from the chamber on Monday for Mr Cameron's statement on the Brussels summit and joining his MPs in a mass abstention on a motion congratulating the PM, Mr Clegg was greeted with mocking cheers from Labour MPs as he took his seat.
Mr Miliband said that Mr Cameron had promised the coalition Government would operate in a "collegiate" way, and asked: "What's gone wrong?"
But Mr Cameron - buoyed by a notable boost in the polls since the dramatic events of Friday morning - retorted: "No one in this House is going to be surprised that Conservatives and Liberal Democrats don't always agree about Europe...
"I make no apology for standing up for Britain."
In Berlin, Mrs Merkel sought to mend fences with London by saying it was "beyond doubt for me that Great Britain will in future continue to be an important partner in the European Union".
She indicated she has not given up hope of eventual UK involvement in the new compact, telling the German Parliament that it remains open for all EU members to join and it should be merged with the official treaties as soon as possible.
But Downing Street said its position had not changed and Britain would only sign up if it obtained safeguards for the City of London which were roundly rejected last week.
Mrs Merkel also risked alarming British eurosceptics by saying that, as a result of last Friday's agreement, "the vision of a genuine political union is beginning to take shape". A new sense of shared responsibility and destiny across the 17 eurozone states and the EU's other 10 members "will far outlast this crisis", she said.
Mr Clegg too was trying to rebuild bridges, meeting a group of pro-European business leaders to assure them that the Government is "absolutely determined" to ensure that Britain remains at the heart of the European single market.
He acknowledged "differences of view" between the two coalition parties, but told members of Business for New Europe - including Tory peer and former European Commissioner Lord Brittan - that he spoke "on behalf of the whole coalition Government" in maintaining the importance of Britain's place in the EU.
"The 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 in the weeks and months ahead," said Mr Clegg.
After a vituperative response to Britain's veto in the European Parliament, he wanted to ensure that "our calm, reasoned and engaged voice is heard positively within the EU institutions in the period to come".
In the Commons, Mr Miliband made fun of the Liberal Democrat leader, who was woken in the early hours of last Friday to be told how Mr Cameron had blocked the treaty.
"I think our sympathy is with the Deputy Prime Minister," said the Labour leader. "His partner goes on a business trip, he is left waiting by the phone and he hears nothing until a rambling phone call at 4am confessing to a terrible mistake."
But the PM said Mr Miliband had failed to make clear whether he would have signed the proposed treaty, and turned his accusations of a rift with Mr Clegg back against him by highlighting his own differences with brother David.
"He shouldn't believe everything he reads in the papers," the Prime Minister told MPs. "It's not that bad - it's not like we're brothers or anything."
BNE chairman Roland Rudd said that members of the group were concerned at the position Britain has been left in by the use of the veto, and by Mr Cameron's threat to deny the new compact use of EU institutions like the European Commission and European Court of Justice.
"Business clearly wants a deepening and widening of the single market and that is what our message is in terms of wanting to see greater reforms," said Mr Rudd. "I think people are concerned about the position we are in but they are encouraged at what they have heard recently."