Relations between Britain and France were at their lowest ebb in years as London and Paris traded accusations over the state of the two countries' economies.
The tensions were inflamed when Nicolas Sarkozy's Finance Minister became the latest in a series of senior French figures to attack the British Government's handling of the economy.
François Baroin said yesterday: "The economic situation in Britain today is very worrying and you'd rather be French than British in economic terms. We don't want to be given any lessons and we don't give any."
David Cameron has not spoken to Mr Sarkozy since the French President described him as an "obstinate kid" after their public falling-out seven days ago. By contrast, Mr Cameron has discussed the eurozone's problems with several EU leaders – including the German Chancellor Angela Merkel, who telephoned Downing Street yesterday.
Nick Clegg, the Deputy Prime Minister, told the French Prime Minister that the latest comments were "simply unacceptable" and urged him to "calm the rhetoric".
Earlier, Downing Street had responded to the French attack by pointing to the UK's ability to borrow money more cheaply on the international markets as a sign of confidence in British policy. Far from smoothing over their differences since those fraught negotiations, the acrimony between the two governments appears to have intensified. It dates back to last month when George Osborne suggested that France could be the next EU country to face a debt crisis.
Despite emerging isolated from last week's summit in Brussels, Britain is cautiously optimistic of building a new alliance with Germany in talks over the future of the single currency.
The French Finance Minister took his swipe at the British Government hours after being warned that his own country was about to slide back into recession. The French government is furious over suggestions that its credit rating should be downgraded from its cherished AAA status, blaming Mr Cameron's stance for undermining confidence in the EU's ability to get a grip on the crisis.
Downgrading would be a grievous blow to Mr Sarkozy, who is trailing in the polls ahead of an election in March and is pinning his hopes of a second term as President on being able to demonstrate that he is charting a clear course out of the crisis.
François Fillon, the French Prime Minister, and Christian Noyer, the Governor of the French central bank, have suggested that Britain is a more suitable candidate for being downgraded because it has a greater deficit and weak economic growth.
Mr Cameron's spokeswoman dismissed Mr Baroin's claims and pointed to the low bond yields – the rate at which a country can borrow over a long period – being offered to the UK Government. Britain is able to borrow money over 10 years at a rate of about 2 per cent, compared with a rate of about 3 per cent for France.
She said: "In terms of our economic plan, we are very clear: we have a plan endorsed by numerous international organisations and the bond yields underline the credibility of the plan."
The Tory MP Andrew Tyrie, chairman of the influential Treasury Select Committee, said yesterday: "The plain fact is the UK is in a somewhat better position." He warned that "trying to distract attention to other countries' problems is not going to help anyone" and said he was "a bit surprised and disappointed" that Mr Noyer had joined the French attacks on Britain.
Mr Fillon broke off from a visit to Brazil to ring the Deputy Prime Minister, whom he has met several times, in an attempt to lower the diplomatic temperature. A spokesman for Mr Clegg said Mr Fillon had reassured him that he had not intended to call Britain's credit rating into question.
"The Deputy Prime Minister accepted his explanation but made the point that recent remarks from members of the French government about the UK economy were simply unacceptable and that steps should be taken to calm the rhetoric," the spokesman said. The men agreed to speak again shortly to discuss economic co-operation.
Meanwhile, a draft version of proposals for a fiscal compact to govern the eurozone emerged in Brussels. Under the plans, a summit of members would take place twice a year and countries that run up large deficits could be brought before the European Court of Justice.
The 700 Year Bitch: The Worst Insults
Jean Froissart (1333-1410)
"The more blood they [the English] shed, the crueller and more ruthless they become."
Francois Rabelais (c1494-1553)
"Sot comme un Anglois." [Drunk as an Englishman.]
Bishop Jacques-Benigne Bossuet (c1494-1553)
"Ah, la perfide Angleterre..."
Napoleon Bonaparte (1769-1821)
"The English are a nation of shopkeepers"
"The English are, I think, the most obtuse and barbarous people in the world."
Charles de Gaulle (1890-1970)
"Non." (Vetoing the UK's bid to join the European Economic Community in 1963.)
Jacques Chirac (2005)
"[Tony Blair] is pathetic and tragic ... worse than Thatcher, just as arrogant but selfish too."
Bernard Delanoë (2005)
After London won the right to host the 2012 Olympics, the Mayor of Paris complained: "The victory was won by other means than Olympic ones."
Francois Fillon (2011)
The French Prime Minister, said on Thursday: "Our British friends have a higher deficit and debt [than us] but it seems the ratings agencies have not yet noticed.
Nicolas Sarkozy (2011)
A frustrated French President revealed in a magazine interview this week that he thought David Cameron "behaved like an obstinate kid, with a single obsession: protecting the City. No country supported him. That is the mark of a political defeat. I manoeuvred well."