Deputy Prime Minister Nick Clegg has launched an attack on David Cameron for "isolating" the UK in Europe with his veto of changes to the EU treaty.
Sources close to the Liberal Democrat leader said he did not feel the failed eurozone crisis negotiations had resulted in a good deal for the UK.
The BBC understands Mr Clegg was dismayed when he was woken early on Friday to hear of the PM's decision.
Initially Mr Clegg said the coalition government was united in its position But now sources close to him have confirmed that he "doesn't think this is a good deal for Britain".
Mr Clegg "couldn't believe it", they said, when he was told the summit in Brussels had "spectacularly unraveled".
BBC political correspondent Robin Brant says the comments linked to Mr Clegg mark a considerable change in tone from Friday when he said he and Mr Cameron had worked together on the UK's negotiating stance.