Deputy Prime Minister Nick Clegg has said Britain is unlikely to join the euro during his "political lifetime".
Mr Clegg - whose Lib Dem party was at the forefront of the pro-euro campaign - said the currency might have avoided its current debt crisis if the rules governing it had not been "flouted".
And he refused to rule out British entry at some point - but conceded it was currently "off the horizon".
Vince Cable has meanwhile insisted the euro could still be a "success".
The Lib Dems have long been enthusiasts for joining the European single currency, saying in their 2010 general election manifesto that it was in the UK's "long-term interest".
They were forced to water down this ambition when they entered government with the Conservatives, with the coalition agreement ruling out a referendum on Britain's entry until at least the end of the current Parliament in 2015.
And they have been forced to row back still further amid the ongoing debt crisis in the eurozone - and predictions from economists that the single currency is doomed in its current form.
Mr Clegg, a former member of the European Parliament, has conceded that "with the benefit of hindsight... it would've been huge, huge error" for Britain to have joined the single currency, which was set up in 2002.
But he said the crisis could have been avoided if the member states such as France and Germany had followed the rules.
He told BBC News: "I don't think anyone could have predicted at the time that the euro was created that the rules which were supposed to be in place to ensure that everybody kind of looked after their own financial affairs properly would be so spectacularly ignored and broken.
"And I think history will judge the then French and German governments very, very unkindly who, some years ago, basically signalled that the rules could be relaxed because that then sent a signal out to everybody else that we don't really need to keep our house in order. And now I think we are dealing with the consequences."
Mr Clegg, whose party is holding its annual conference in Birmingham, was pressed on when whether he thought the Lib Dems would ever again call for Britain to join the euro.
He said: "I'm going to lead this party for a long time, I hope. I'm not going to hold my successor's hands...
"[But] I doubt very much in my political lifetime, certainly as leader of the Liberal Democrats, that we will see this country entering the euro."
He added: "I cannot speculate on whether, if we had been in the euro, we might have made sure that the rules had been respected."
Former Lib Dem leader Lord Ashdown - another one-time advocate of monetary union - told The Spectator magazine - he did not believe the euro could continue in its current form, predicting instead that a "core euro" would be set up, with Germany, Austria, Finland, Belgium, the Netherlands, Luxembourg and France among its members.
It would be essential to "create the institutions to govern" the currency effectively, he added.
Business Secretary Vince Cable told BBC Two's Newsnight on Monday that it "doesn't make sense" to talk of joining the eurozone currently, and that his party had only ever advocated doing so when the economic conditions were right and after winning a UK-wide referendum on the matter.
But he added: "The eurozone project may turn out to be a great success. We don't know... It's foolish to use the word 'never'."
However, another former leader, Sir Menzies Campbell, appeared more certain than Mr Clegg about Britain's position, had it joined.
He told told the BBC it would have "exercised the kind of discipline that we have seen in Germany, which has profited under the euro".
Divisions Europe have also surfaced among Conservatives, with Prime Minister David Cameron on Chancellor George Osborne calling for greater fiscal integration in the eurozone - putting them at odds with backbench eurosceptics.
'Tea Party' warning
In his speech to the Lib Dem conference, Energy Secretary Chris Huhne Chris Huhne launched a scathing attack on the Tory right, bracketing them with the "madcap" American Tea Party movement and warning they will "wreck the nation's economy".
The Energy Secretary used his speech to round on Conservatives who "slaver over tax cuts for the rich" and claimed if they failed to compromise Britain's economic recovery would be "put in peril".
On Europe, he said: "If you fail to compromise, if you fail to seek the common ground that unites us, if you insist that only you have the answers, if you keep beating the anti-European drum, if you slaver over tax cuts for the rich, then you will put in peril the most crucial achievement of this government.
"You will wreck the nation's economy and common purpose. We are all in this together and we can't get out of it alone."
In the latest development in the eurozone crisis, Italy has had its credit rating cut by agency Standard and Poor's from A to A+, potentially making it more expensive for the Italian government to pay off its debts.
The surprise move by the ratings agency will fuel fears of contagion in the eurozone.
Italy has Europe's second-largest debt level and the cost of that debt has been rising in recent weeks as lenders to Italy have become nervous about its ability to repay loans.