BRUSSELS -- The introduction of the euro in 12 of the 15 member states of the European Union has been an unqualified success. The changeover had none of the hitches and glitches that many -- including myself -- thought would mar its early days.

To everybody's surprise there was no mass hysteria as people pocketed their change in euros, no chaos among cashiers in Europe's shops and supermarkets, no flood of counterfeit money to undermine global confidence in the currency -- no ammunition for Britain's xenophobic tabloid press in its drive for English isolationism. Instead it all went so well that the euro became positively fashionable.

This trend has diminished somewhat with the passage of time, but the job has been done: The successful single currency has arrived. Yet it is this very success that poses an enormous dilemma for British Prime Minister Tony Blair. Britain can no longer hide behind the procrastination of "wait and see."

Others already see the writing on the wall. In two of the three "hold out" countries, public opinion is positive and governments are bending to the new reality. Denmark is promising a second referendum on formal membership in the euro zone -- the first was lost 53 to 47 percent in September 2000 -- while the Swedes, reluctant to put the matter to the public after the initial snub by the Danish electorate, will now take the plunge with or without their Scandinavian neighbors. All of which threatens to leave Britain isolated in the EU.

Britain cannot afford to go it alone. The continuing decline in inward investment and the decline in manufacturing, both seriously affecting jobs and prosperity in this country, has led to industrialists arriving in Westminster in droves to lobby the government.

The latest batch, representing more than 20,000 print workers, say they need progress now or jobs will go. Blair is convinced, but the last defense for dithering, as British influence in EU economic and monetary policy dribbles away, is the famous five economic tests that Chancellor of the Exchequer Gordon Brown persuaded the Cabinet to check before the government fired the starting gun for the British referendum.

Many saw these conditions merely as a temporary technical fix to a political problem. During last June's election campaign a test score card was promised within two years, and today a team of Treasury civil servants are starting to make the assessment.

Of course, the economic conditions will have to be right for membership. No one would dispute that. But why should Britain not be ripe for membership? British economic policy has been a model of orthodoxy within the current neoliberal paradigm. The economy, in the most quantitative measures, is slap-bang in the middle of the EU pack.

If the euro fits Greece and Germany, France and Finland, Italy and Ireland, it shouldn't have too much trouble accommodating Britain. The problem is facing down Gordon. To do that requires belief the referendum can and will be won, because to fight and lose would threaten not only Blair's and the Labour government's future, but the unity of Britain.

Current thinking within the Britain In Europe campaign -- the all-party pro-euro group -- is that the post-introduction shift in public opinion, with a sharp rise in support for membership, and a majority believing membership is inevitable, has enabled the skirmishing to start.

Euro supporters believe this shift in opinion will be consolidated by the 30 million trips that Britons will make into "Euroland" this year, becoming familiar with the euro and its advantages both in terms of price transparency and its enormously enlarged spending footprint.

In early autumn, the five tests will be cleared and the necessary legislation to enable a referendum to take place will be ready. That will be the point of decision for Blair, after which there can be no retreat. It should be easy -- if the prime minister retains his nerve and his authority. Everything is in our favor.

The pro-euro campaign has momentum, the middle ground, positive messages and an intellectual underpinning. When the most popular postwar prime minister puts his support behind a referendum, the campaign will have national leadership.

A united Labour Party with support from the Liberal Democrat Party, the trade unions and the bulk of industry can roundly defeat a divided Conservative Party allied with the rag, tag and bobtail of the xenophobes, nostalgics and the political and economic equivalent of the Flat Earth Society.

The problem is the siren voices of skeptics within the Labour Party. To lose would inevitably mean the end of Blair's tenure at 10 Downing Street. Labour's hold on power would be enormously weakened. After the Norwegian Labour Party was defeated in the last referendum on EU membership in November 1994, Gro Harlem Bruntland swiftly departed and Labour lost power for the first time in generations.

It would be difficult to imagine, with party affiliation among the electorate at an all-time low, that British Labour would not suffer the same fate. A defeat would be exacerbated by the likelihood that Scotland, Wales and Northern Ireland (already returning polls showing a majority in favor of joining the euro) will vote yes with the support of "nationalists" in and outside the Scottish National Party and Plaid Cymru. That would result in renewed pressure for independence, with the voters whipped up by an English veto blocking Scottish and Welsh aspirations concerning Europe.

These fears may be realized if Labour leaders and members do not think through the consequences. The risks should be enough to restrain those who, jockeying for succession to Blair, think that pulling their anti-euro punch during the campaign might leave them well placed to succeed him if the electorate failed to go with the flow. Have they already forgotten that it is better for them -- and the people of Britain -- to be senior figures in a Labour government rather than leaders of a discredited opposition with few prospects of a swift return to power?

Equally, Labour's disgruntled rank and file, with unrealistic expectations fed by 18 years in opposition, married to a government determined not to be labeled by Labour's history, might be tempted to help trip up Blair. That would be an equally catastrophic error.

Does anyone believe that it would not be Ian Duncan Smith and his rightwing Tories who would reap the benefits of the whirlwind of defeat? Does anyone seriously believe it would lead to a continuing Labour government with a new more leftwing, more socialist leader? Certainly not anyone living in the real world of electoral politics.

The final temptation is to prevaricate, to make indecision a principle in itself. This will be as dangerous. Britain and the electorate will soon smell the fear that self-interest and cowardice demonstrate. If we make the brave choice, Labour will win and gain authority that can be used to transform Britain's future in ways seen as dangerous until now.