David Cameron has attempted to rally support among European leaders believed to have deep concerns about last week's summit deal amid reports French President Nicolas Sarkozy made a savage personal attack on his leadership.
The Prime Minister told Tory MPs he was in close contact with counterparts in other member states and insisted it was "not one against 26", party sources said.
But tensions between the UK and France were heightened further on Wednesday night after an unconfirmed report in French satirical magazine Le Canard Enchaine suggested President Sarkozy had accused Mr Cameron of behaving "like an obstinate kid".
The magazine reported that Mr Sarkozy told his party's MPs in a private meeting that he had achieved a "good coup" by securing an agreement covering most of the EU while resisting the UK's demands.
"It's the first time that we have said 'No' to the English," Mr Sarkozy is reported to have said. "Cameron behaved like an obstinate kid, with a single obsession: protecting the City, which wants to carry on behaving like an off-shore centre. No country supported him. That is the mark of a political defeat.
"Objectively, it was a good coup. I manoeuvred well. The whole world recognised that my proposal was the only possible course. The accord will perhaps not put an end to the crisis, but it is a tool for facing up to it. The dynamism of the Franco-German axis enabled us to rally 26 countries."
No 10 confirmed Mr Cameron made calls to leaders in the Czech Republic and Sweden - two non-eurozone nations that could waver when it comes to signing up to the summit deal - as well as Irish prime minister Enda Kenny, who has warned a referendum may be needed on the deal.
Downing Street said Mr Cameron "reiterated the UK's position that he had been ready to agree treaty change for the EU provided the UK secured some modest and practical safeguards to protect the single market". "In each call the leaders agreed to build on their close co-operation on EU issues, especially promoting jobs and growth through the single market," the spokesman said. "They agreed that the priority for the European economy remained comprehensive and decisive action to deal with debt and increase competitiveness."
In Berlin, Chancellor Angela 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.