Hollywood has long known the truth that “nobody knows anything”, but politics is only just getting its head around the idea. Just as no studio boss can ever know which film will hit and which will miss, so the sages of the political trade are beginning to speak with, if not quite humility, then at least caution.

This new-found hesitation has three causes: Scotland, the general election and Jeremy Corbyn. The experts did not see the yes surge coming in last year’s referendum; the pollsters swore 7 May would produce a hung parliament; and not one commentator predicted Corbynmania.

Perhaps it’s a paradox too far to try to predict the next big surprise, but given recent experience few would want to call the coming referendum that will determine whether Britain will remain in the European Union. The only safe bet, one that expects the unexpected, might be to reckon that the current tide of anti-establishment populism – washing away certainties on both sides of the Atlantic, from Syriza to Donald Trump, from Podemos to Bernie Sanders – will come in hard when Britons vote on their European future.

The latest polling has in ahead of out – but the margin is narrow: 44% to 39%

Given that staying in the EU is by definition the status quo option, and that the prime minister and chancellor are likely to be among its most prominent advocates, then voters in a mood to show two fingers to the elites will surely be drawn to the cause of out. The question is, how strong will that tide be – and what can the “remain” campaign do to beat it back?

They’ll have their work cut out. The latest polling has in ahead of out, but the margin is narrow: 44% to 39%, according to ICM. That’s a far smaller lead than no held over yes in Scotland this far from the vote, only to see that advantage sharply reduced once battle was joined. In effect, this race is neck-and-neck from the start.

The leavers, who formally launched their campaign today, have some built-in advantages. They can justifiably count on most of those 4 million voters who backed Ukip in May. Many Conservative voters will lean their way too. (Certainly among Tory activists, if this week’s party conference was anything to go by, the energy is all for out: the Conservative prepared to make a vocal case for the EU has become a very rare bird.) Committed leavers have concluded that the core battleground is the centre and especially the centre-left: they reckon it will be Labour voters who will decide the referendum.

And here too the new terrain seems to offer an opening for out, and not only because the Labour leader will struggle to be even a lukewarm advocate for the other side. For a long while, pro-Europeanism was a reflex on the left. Much of that was negative: a rejection of Faragism and the apparently obsessively nostalgic Little Englander mentality that defined British Euroscepticism for the past two decades. Much of it was cultural. For those who wanted to be modern and cosmopolitan, outward-looking and tolerant, warmth towards Europe was part of the package. That became truer still when Farage became the face of anti-EU sentiment, making it into a proxy for hostility to immigration.

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But that might be changing. “Greece vindicated the classic Bennite critique of the European project,” says Daniel Hannan, a Tory MEP and one of the sharpest voices in the out camp. “Here was a leftwing, democratically elected government being bullied by Brussels.” The core argument associated with Tony Benn – which defines democracy as the ability to kick out those who truly rule over you – has gained a new currency thanks to the Greek crisis, Hannan adds.

The proposed TTIP agreement, which could see corporations overturning laws and policies passed by democratic governments, and the prospect of yet more mandatory privatisations of public services, has made the left look anew at the EU – and not in a kind way. “Better a bad parliament than a good king,” Benn used to say. For him, even benign rule by a monarch was worthless because the king’s whim could change and there’d be nothing you could do about it. This is the argument the leavers will revive, to woo the centre-left: that the Delors-era, when the EU was associated with workers’ protection and the “social chapter,” is over, that Brussels is now the friend of the megabanks and the multinational corporations, and it’s out of democratic reach. It may well resonate. Note that signed up to the leave campaign is the Green peer Jenny Jones. As for immigration, the leavers even have a left-friendly version of that. They’ll say that the EU’s freedom of movement policy means Britain can, in effect, only take in (mainly white) migrants from Europe, thereby excluding (often non-white) newcomers from the commonwealth. The Birmingham Labour MP Khalid Mahmood is an outer for that reason.

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How can the remainers fight back? They are aware of the dangers. They know that if their public face consists solely of politicians and business leaders – and their chair is to be the Tory peer and former M&S boss Lord Rose – they will look like the establishment. To avoid that, come their launch on Monday, they hope to unveil some celebrity advocates too. They will frame the contest as a choice of two competing visions of Britain, knowing that if it is cast as Britain v Europe – the way Better Together sometimes allowed the 2014 choice to become Scotland v Britain – they will be on the losing side. Though they have some killer facts to deploy, they promise not to rely on a blizzard of trade figures but also to make an emotional appeal to Britain’s long history of engagement with the wider world, which they say made this country great.

That said, they calculate that sandwiched between the idealists on both sides – for in and for out – is a large body of pragmatic Britons whose vote will be based on a hard-headed, transactional calculation of largely economic self-interest. If, after a long campaign, say the remain camp, the two sides have fought each other to a draw on the net costs and benefits of EU membership, fear of the unknown will tip these uncommitted voters towards in. People will not want to take a step into the dark.

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But none of that alters the awkward fact that the leavers will have a populist wind at their back. Every time a figure in a suit, whether politician or corporate chieftan, warns the public of the catastrophe that will descend upon them should they vote out, there will be new recruits to the out cause – if only to poke a finger in the eye of the hated powers-that-be.

The remain campaign is betting that, even if such a dynamic kicks in, it will not be decisive. Yes did unexpectedly well in Scotland, but it didn’t win. For all the insurgent energy stirred by Ukip, the Tories won the general election. And yet, the possibility is strong that the era of Tory dominance now under way will be a tale of two unions, both rent asunder: that the United Kingdom will break out of the EU, a move that will in turn break up the United Kingdom. British politics is in such flux, even the future shape of the country is uncertain.