A poll on the euro could be held before the next general election, Tony Blair has said as he launched what he called a "gear change" in government campaigning on Europe.
The prime minister was speaking at a joint press conference with Chancellor Gordon Brown aimed at talking up the benefits of euro membership and making the "patriotic case" for Britain's role in Europe.
The event comes the day after Mr Brown announced the government's view that the time was not right for the UK to join the euro.
And it is being seen as an attempt to counter suggestions that the euro verdict means Labour has gone cool on Britain's role in Europe.
Mr Blair said a referendum on the currency before the next election was a "possibility" and that there was "a realistic prospect of progress".
But he added: "We will have to make a judgement on what happens in the coming year."
He went on: "The path is clear, this is something we want to do, we have a process in place."
But he said Britain should only take that step when the economic conditions were right.
The prime minister said the euro statement on Monday - in which Mr Brown said he would reassess the case for joining the euro next spring - marked a "definitive change" in the process by making the benefits of euro membership clear.
'Change of gear'
Mr Brown said he and Mr Blair would put the "patriotic case" for Europe, taking on the "myths and prejudices" about membership of the EU and the euro.
He said they would show that being part of the EU did not mean turning away from the US or allowing national values to be "submerged in Europe".
He said MPs were being sent a letter setting out the pro-euro case and the reforms needed to clear the way for UK entry.
And he said there would be a series of roadshows in which Mr Blair and Mr Brown would seek to boost support for euro membership.
Mr Blair - promising "a definitive change of gear" in the government's approach to the euro - admitted that politics would play a big part in the debate, saying the government would work to bring a "strong pro-Europe consensus in Britain".
He said: "It is time to make the argument for Britain in Europe, to take on those who believe if we are pro-British, we must be anti-European...
"To defeat the false case that if Britain is a full-hearted member of the EU we lose
our identity as a nation.
"And to show, in a world that is moving closer together and being transformed by globalisation, it would be a cruel denial of our own proper self-interest to cut ourselves adrift from the major strategic and
economic alliance right on our doorstep."
The UK's five tests
NOT MET: Convergence with eurozone
NOT MET: Enough flexibility to adapt
NOT MET: Impact on jobs
MET: Impact on financial services
NOT MET: Impact on foreign investment
Asked whether the euro decision was tied up in an alleged agreement that Mr Blair would eventually step aside as prime minister in favour of Mr Brown, he said he wanted to deal with "not the soap opera, but the issues".
He said: "There are on either side of this argument, I think, simplicities that are
"Sometimes, when people see it through the prism of the two of us, they are seeing it in that way because they are actually wanting to avoid what are genuine questions on either side of this argument."
Earlier, the chancellor said he believed "substantial progress" could be made to ensure the British economy is in a position to start the process of joining the single currency in 2004.
But the opposition parties say Mr Brown and Mr Blair are split on the euro issue, with the news conference seen as an attempt to show this is not the case.
Tory spokesman Michael Howard said the euro decision was "looking more and more like a shoddy political fix between Mr Blair and Mr Brown".
He went on: "The national economic interest is coming a poor second to Labour's bitter and personalised faction fighting. The ambitions of two men are coming before the needs of our nation."
The pro-euro Liberal Democrats fear Mr Brown has offered "warm words" instead of real action to prepare for euro entry.