London: It is the summer of 2015. The polls have been proved right. In another low turnout election, Ed Miliband has led Labour back into government by a slim majority. Standing outside No 10, the new prime minister faces the cameras and declares: “Our task is to restore growth to the economy and hope to Britain.” Not for the first time, Labour has come to office confronting a struggling economy but with only a fragile electoral mandate to take action.

So the most pressing task for the Miliband government is obviously to hold a referendum on Britain’s membership of the European Union, right? Wrong. Absolutely, and in all foreseeable circumstances, wrong. The Labour government, if there is one, will not have the luxury of a landslide victory to cushion it. It will stand or fall on its record of management of a sluggish economy. Raising the prospect of leaving the EU will damage the economy further. It is a risk that has the potential to shipwreck any government.

The next Labour government will not have the luxury of wasting its capital on secondary issues. Europe, in this context, will indeed be a secondary issue. That is not to say Europe’s future will be unimportant in the Britain of 2015. On the contrary. Nor is it to say that in 2015 nothing will need to be reformed in or concerning the EU. That would be wrong too. Least of all can Labour afford to pretend that Europe can simply be ignored. That is why, over Europe, as over Scotland, its slogan should be Better Off Together.

But Europe is categorically not the issue that defines what the Labour party exists to do, either now or in 2015. If Labour is elected in 2015 it will be because the voters want it to fix the economy, and do its best to protect the vulnerable. In spite of everything that has changed in the world and in politics over the past half-century, Labour remains fundamentally a party of social justice. It is a patriotic party too, but it is not an ‘ourselves alone’ nationalist party like the SNP, Ukip or, increasingly and tragically, the Conservatives.

Labour needs to keep its collective mind very firmly fixed on the realities of 2015 this week. It needs to do this because its effectiveness as a governing party over the next few years depends on it. Labour’s ability to shape the post-2015 agenda is best served by not being bounced into promising a referendum on Europe as a result of the hoopla surrounding David Cameron’s speech on Europe on Friday. To do that would be to concede, even in government, to the Conservatives, and to what is often the worst press in the western world.

The pressure to make such a promise should not be underestimated. Cameron gave a foretaste of this in the mischievous and misleading manner in which he framed 2015 in his exchanges with Miliband in the House of Commons on Friday. The choice in 2015, said Cameron, would be between joining the single currency and handing power to Brussels under Labour or staying out of the euro and repatriating powers under the Tories.

No, it won’t. Cameron’s characterisation was shoddy stuff. However, it is the one into which the Conservative party’s neurotic obsession with Europe, and the prime minister’s historic failure to deal with it, have driven him. And it is one for which the Tories will receive turbo-charged support from the overwhelmingly anti-European media.

Starting tomorrow, they will frame the European issue as one in which the Tories have at last agreed to let the people decide. Now, Miliband, they will ask, where do you stand? With the people or against them?

To stand against this will be a tough ask. In the recent past, Labour’s instinct has been to triangulate around such awkwardnesses. Even today, the party’s muscle memory may be telling it to kill the issue by over-trumping the Tories on Europe and promising an in-out referendum of its own. One or two lifelong Labour pro-Europeans have been tempted into this camp, while some others see this as the kind of pledge which would signal that Miliband’s Labour is not an elite project they charge New Labour with being.

Yet stand against it Labour must. Miliband must. The shadow cabinet must. They must do it for the reasons set out by the shadow foreign secretary Douglas Alexander in a characteristically thoughtful speech. And they must also do it for the simple reason that rebuilding a viable economy, not the relationship with the EU, is the pre-eminent issue facing modern Britain. The party may take some short-term hits in the polls for not slipstreaming behind Cameron on Europe in the coming weeks. They must expect the Conservatives to get a temporary poll boost from tomorrow. But they should not panic. Such polling spikes have come and gone on Europe before. In the end, the election will be won and lost on the economy.

And rebuilding a viable UK economy is simply not compatible with leaving the EU. Leaving the EU makes the economic task far harder. Even creating uncertainty about it has that consequence, too. Most people know this, and even the opinion polls on Europe, which are currently quite volatile, recognise it. That is why Cameron’s weakness in allowing the Tory party to become so obsessed with Europe is ultimately so significant and, for him, so damaging.

Indeed, it begins to look as though the unwinding of British party politics may play into Labour’s hands. It has at least presented Labour with a genuine opportunity to again become both the national party and the natural party of government. How many parties in British politics can talk plausibly — and with the prospect of representing them — to audiences in England, Scotland, Wales, as well as to Europe? Only Labour can do this. It is the only party in UK politics which can claim to be a national party.

Whether Labour can take advantage of what is on offer to it is not clear. The credibility of the party’s economic strategy will be decisive. But Labour will not succeed if it allows itself to be diverted from its core tasks on the economy and social justice.

In the 1980s, Labour paid the price for being deeply split over Europe in the 1970s, when cabinet minister slugged it out with cabinet minister in the 1975 referendum campaign. It took nearly 20 years for Labour to recover. Today, it is the Conservatives’ turn to flirt with such schisms. Labour has a lot to gain if it can hold its nerve. The prize, for a political party, is the only one that matters.