British membership of the euro is now a question of "when, not if", a leading minister has claimed.

In an interview with ePolitix.com, Europe minister Denis MacShane said the balance has tipped towards inevitable membership of the single currency.

Saying the UK is at a "turning point", MacShane warned that Britain will squander its competitive edge by staying out of the euro.

"After the chancellor's statement on June 9, the question of joining the euro becomes when, not if," MacShane told this website.

Despite suggestions that the fall-out from the Iraq war has derailed the euro campaign, the Foreign Office minister argued that the case for membership should be put forward "very forcefully" by the prime minister and the chancellor.

"I think all ministers and all MPs who have a regard for the national interest. have got to defeat the anti-European and isolationist politics that we're now seeing from the leadership of the Conservative Party," he said.

Signalling that the prime minister has not lost his appetite for a concerted pro-euro campaign, MacShane told ePolitix.com: "Anybody who's known Tony Blair, anybody who's looked at any of his speeches on Europe since he became prime minister will see a man who understands the necessity for Britain to be in Europe and helping to run Europe".

The prime minister is "a man who's very comfortable with the new enlarged European Union...and a man who understands for Britain to remain isolated in eternity from a currency that 250 million Europeans are using...would be a huge mistake".

Rejecting suggestions that the campaign was now off the agenda, MacShane insisted that the pro-euro roadshow could take to the streets within 24 hours.

"I have got articles that can go into every newspaper in the country tomorrow, I'm prepared to go on television every night to make the case for Europe," he added.

But he warned that "our national media have got their own news agenda".

"A significant part of the media are anti-European and even some of the newspapers who are culturally pro-Europe are very hostile to an honest discussion on the euro," conceded MacShane.