Newspapers quoted sources close to Deputy Prime Minister Nick Clegg as saying he was angry with David Cameron for vetoing a new EU treaty, in an apparent sign of widening cracks in the coalition.
In public, the Europhile Clegg has publicly backed Cameron, saying Britain made reasonable demands at the European summit on Friday and the coalition was united on the issue.
But the Independent on Sunday quoted sources as saying Clegg was privately furious.
Nick certainly doesn't think this is a good deal for Britain, for British jobs or British growth, a source described as close to Clegg was quoted as saying.
It leaves us isolated in Europe and that is not in our national interest. Nick's fear is that we become the lonely man of Europe, the source said.
His party officials said they had no comment on the reports.
Britain was sidelined on Friday as the other nine EU countries outside the currency bloc said they were prepared to back the 17 euro economies in a new treaty, although some sounded notes of caution.
The Independent and the Observer said Clegg believed isolation from the EU's other 26 member states threatened Britain's relations with the U.S., weakened protections for the City of London and put in jeopardy future foreign investment in the UK.
Business Secretary Vince Cable expressed concern on the record that Britain had scored an own goal.
He told The Sunday Telegraph: I am not criticising the prime minister personally. Our policy was a collective decision by the coalition. We finished in a bad place.
A clutch of Liberal Democrats have criticised Cameron's stand, warning it will leave Britain out in the cold, while jubilant eurosceptic Conservatives have stepped up calls for a full renegotiation of Britain's position in the EU.
On Saturday chancellor George Osborne said that Cameron had taken a tough decision but that it was the right one.
(Reporting by Stefano Ambrogi; Editing by Andrew Roche)