Chancellor Gordon Brown has concluded the UK is not yet ready to join the euro, the BBC has learnt.
Prime Minister Tony Blair has accepted the chancellor's view, though the finer details of an official announcement - which could come as soon as next week - are still being worked on.
But Mr Brown's ruling is that the UK has not passed his five economic tests for joining the currency.
A further key decision - when to assess the tests again - has yet to be reached.
Responding to the BBC story, Downing Street was quick to play down news a decision had been taken.
"The government has nothing to say on this topic until the economic
assessment is published," a spokesman said.
Welsh Secretary Peter Hain said the decision process was in "the end game" but that no final decision had been made.
But the Tories leapt on the BBC report by political editor Andrew Marr, with shadow chancellor Michael Howard saying it showed that a "fudged decision" would be made by Mr Brown and Mr Blair based on "personalised faction fighting within Labour".
"It is time Labour put Britain's national economic interest first before their own internal factions," he said.
Lib Dem spokesman Matthew Taylor said: "It is clear that the Treasury has briefed against the prime minister in an
effort to bounce him into a decision that has not yet been finalised."
Mr Blair has held days of intensive discussions with Mr Brown and is understood to have agreed the time for joining is not right.
HAVE YOUR SAY
Go with the future and stop living in the past
Connaire McGreevy, Northern Ireland
The chancellor was widely believed to be reluctant to recommend euro entry, but it is the fact that the prime minister appears to have accepted his chancellor's assessment that is most significant.
Andrew Marr said: "The prime minister has accepted that economics must be paramount and the economics remain negative."
He added that joining the single currency remained the "single biggest decision of Tony Blair's premiership".
Mr Blair has always been an enthusiastic advocate of Britain's eventual membership and it is understood that both politicians are still discussing whether to leave the door open for a further assessment before the next election.
Mr Brown is said to favour ruling that out.
One of the economic differences between the UK and the eurozone that is thought to have played a part is a substantial difference in housing markets.
If a recommendation had been made to join then the next step would have been a referendum on the issue of ditching the pound and joining much of the rest of the EU by taking up the euro.
The issue has dominated British domestic politics for years with both the main political parties split on whether or not to join.
In contrast to Mr Blair's enthusiasm is the opposition to joining in the leadership of the Conservatives.
On Wednesday Tory leader Iain Duncan Smith challenged the prime minister to let the British people have their say about Europe's future in a referendum.
The government was due to give its verdict on the five tests for entry by 7 June.
The UK's five tests
Convergence with eurozone
Enough flexibility to adapt
Impact on jobs
Impact on financial services
Impact on foreign investment
The euro is used in 12 of the 15 European Union countries after becoming legal tender in January 2002.
The UK, Sweden and Denmark are the only EU countries still outside the euro.
The key economic test being examined by the Treasury was whether the UK economy has converged sufficiently with the eurozone and whether that convergence was sustainable.
The second test looked at whether there is sufficient flexibility in the UK economy to cope with economic change.
The remaining three tests assessed the impact of joining the euro on jobs, on foreign investment and on the financial services industry.