Lib Dems refuse to back motion praising PM's EU stance
Liberal Democrats have refused to vote on a Commons motion that praised David Cameron's handling of the EU summit.
Tuesday's motion said the use of the veto was a "vital means" to defend the UK's national interest.
Earlier David Cameron had said the coalition government remained "very strong" despite tensions over the EU.
Meanwhile two polls put the Conservatives ahead of Labour for first time this year.
MPs had been debating the issue of Europe in the House of Commons and backed a motion by the Democratic Unionist Party (DUP) - commending Mr Cameron's handling of the issue - by 278 votes to 200.
This was despite the mass abstention of Lib Dem MPs.
BBC political correspondent Carole Walker said the vote underlined stark differences between the Lib Dems and their Tory coalition partners on Europe.
A senior party source said the Lib Dem position was agreed in advance and was consistent with Nick Clegg's assessment that the deal was bad for Britain, our correspondent says.
Earlier Energy Secretary Chris Huhne warned about the dangers of isolation in Europe, saying "playing Billy no-mates is not fun and not effective in promoting Britain's interests".
However, Nigel Dodds, the DUP leader in Westminster, said: "It is time we realised in this House that focusing our foreign policy on the narrow ground of 'greater Europeanism' and ever closer political union in Europe is actually contrary to the UK's vital interests".
Recent events had "brought the day closer" when the public had to have their say on the UK's role in the EU in a referendum, Mr Dodds said.
Labour, who opposed Tuesday's motion, said the prime minister had been driven by party political considerations and had not secured any additional safeguards for the City.
Mr Cameron had struck an upbeat tone after Tuesday's Cabinet meeting - the first since the EU summit.
"The coalition is very strong," the prime minister said. "The coalition came together for a good reason, which was to put aside party interest and to act in the national interest particularly while there are so many challenges facing our economy.
Deputy prime minister Nick Clegg told a meeting of MPs later on Tuesday that "this government carries on until 2015, full stop".
Two polls put the Conservatives ahead of Labour for the first time this year.
A Reuters/Ipsos Mori poll has the Tories on 41% and Labour 39%, with the Lib Dems on 11%.
A Sun/YouGov places the Tories on 41% and Labour on 39% respectively, with the Lib Dems on 10%.
A ComRes/Independent poll puts the two biggest parties neck-and-neck on 38%, with the Lib Dems on 12%.