The chancellor and the prime minister have launched a concerted campaign to sell euro membership to the British people.

Despite ruling out joining the single currency for at least a year, Tony Blair mounted a fresh bid to create a "strong pro-European consensus" in the country.

"It is time to make the argument for Britain and in Europe," he said. "It is time to take on those who argue that to be pro-British we must be anti-European."

"That is our collective purpose on this as a government from now on - to build a strong pro-European consensus in Britain and to do so not as a rejection of Britain in favour of Europe, but, on the contrary, as the proper and modern expression of the true British national interest."

The chancellor added that he and the prime minister "will put the patriotic case for Britain in Europe".

A country-wide roadshow would counter "anti-European propaganda", he said.

"When we take the case into the country from today, we will show the potential benefits of the euro, we will show how Britain's national interest is advanced by our engagement with the European Union, and we will take on anti-European prejudice and myths about Britain's engagement in Europe," said Brown.

"In our speeches and roadshows around the country, we will show how Britain can unite around a pro-European consensus."

Blair hailed Monday's Commons statement as a "definitive change" in the UK's approach to the euro.

"What has changed since yesterday is that first we can now, on the basis of the detailed assessment, be precise about the economic benefits to Britain," he said.

"If we have sufficient convergence, Britain, our families and our businesses, would benefit from being part of a larger and stronger monetary zone."

The prime minister conceded that arguing the case for British membership could prove a long haul.

"This is not a debate that will be won in a day or in a month," he said.

It would have to be "conducted in a far more considered way", the premier told a Number 10 press conference.

On the five tests Blair said there was a "realistic prospect of making progress" over the next 12 months.

And while he conceded that the euro was "controversial", Blair said it would deliver benefits for the people of Britain.

The prime minister stressed that the decision can only be taken on the basis of the economic interests of the country.

"What we have to recognise is that in the end the economic conditions have to be in place," added Blair.

"Of course there are political considerations, there are constitutional considerations but in the end the economics have got to be right."

Quizzed about whether Britain could join the euro before the next election Blair said: "It is a possibility, yes, but the economics have got to be right."

Turning his fire on the Conservatives, the prime minister claimed "they basically are against the European Union as it has developed".

The joint press conference was seen an attempt to play down suggestions that the prime minister and his chancellor are at loggerheads over the government's policy.

But both men refused to comment on the "soap opera" of alleged party leadership pacts.