In a note to investors, SocGen strategist Albert Edwards said: 'My own view is that there is little "help" that can be offered by the other eurozone nations other than temporary, confidence-giving "sticking plasters" before the ultimate denouement: the break-up of the eurozone.'

He added: 'Any "help" given to Greece merely delays the inevitable break-up of the eurozone.'

The alarming claim came a day after European Union leaders promised 'determined and co-ordinated' action to shore up Greece's tattered public finances, but disappointed traders by failing to provide specifics.

Further details are expected early next week, but markets were in high anxiety yesterday amid fears political divisions among rich eurozone members could derail any rescue.

The euro slid almost 1 per cent to $1.357 yesterday, meaning it has lost 10 per cent of its value since November. The pound rose to 1.14 euros.

Earlier this week Business Secretary Lord Mandelson's claimed that the single currency had been a 'remarkable success' and that it remained in Britain's interests to join.

David Cameron ridiculed that claim yesterday.

He told the Tories' Scottish conference: 'Are this Government the only people in the country who still think that would be a good idea? Our deficit and debt are bad enough without the straightjacket of the euro.

'If I am elected for as long as I am prime minister the United Kingdom will never join the euro.'

The French bank's warning was echoed by Mats Persson, Director of the Open Europe think-tank, which campaigns for reforms in Brussels.

He said: 'The eurozone is facing a fully-fledged crisis. The Greece episode has made it painfully clear how flawed the euro project was from the very beginning.

'Even if Greece receives a one-off bailout it would not solve the real problem, which is the huge differences in competitiveness between the eurozone's richest and poorest members.