This article by James Morris, partner and Director of GQR’s London Office, originally appeared in the Times. Tables for the poll mentioned in the article can be found here and the questionnaire here.

 The question printed on the ballot paper has been decided, but the real argument at the heart of the European Union referendum is still up for grabs. The pro-EU side wants voters to think about the risks to trade and jobs if Britain votes to leave. The “out” side wants the referendum to be about identity and immigration. The side that wins the battle to frame the choice is the side that will win the referendum.

 At the moment the “in” side looks confident that the country will line up behind it. The polls this year have seen steady majorities in favour of remaining in the EU; Ukip’s flame has dimmed and, in between other more pressing issues, Angela Merkel has done what she can to signal openness to some of David Cameron’s reform proposals.

 This confidence is dangerously misplaced, and not just because the general election should warn anyone about relying too much on polls to predict what people do at the ballot box. History shows that the single-digit lead for staying in the EU could swing dramatically. In October 1979, there was a six-point margin for “in” — just as there is now. Scroll forwards six months and that had turned into a six-point majority for “out”, just under a year later, “out” was ahead by 60 per cent to 32 per cent.

 As is often the case, the key swing vote on this issue is disproportionately female. Our data shows that two thirds of the people uncertain about which way they will vote are women. It is going to be particularly hard for either campaign to reach this group as they are less likely than men to care one way or another — while one in five men says Europe is one of their top priority issues for government, among women the number is less than 1 in 10.

 The “in” campaign will also need to deal with the enthusiasm gap. Among those who say Europe is one of the top issues for government, “out” leads by 54 points. If this is a low turnout referendum, along the lines of the AV referendum, that margin could prove decisive.

 If the pro-EU side had a slam-dunk argument, it could afford to feel more relaxed. But it doesn’t. Pit the argument for trade and investment against the argument that a crisis-ridden Europe is an economic risk, and the pro-trade side wins by four points. But if the “better-off-outers” can make the case that we can, like Norway and Switzerland, have free trade without free movement of labour, they win by 52 per cent to 35 per cent. The Norway model might sound like a pipedream, but with trust in politicians desperately low, it is hard to know who would have the credibility to prove that point.

 In fact it is hard to find winning arguments for being in the EU. The idea that working with other countries strengthens Britain’s hand in the world is a winner for the middle class and the young, but older voters and working-class voters tend to think that the country would do better if it was less engaged with the world.

 Immigration regularly polls as the top issue facing the country and voters know that the only way to regain direct control of the flow is to withdraw from the EU. The argument that immigration benefits the economy is simply not believed — in a poll we conducted last year, cutting immigration ranked as the best way to boost the economy, ahead of cutting taxes, investing in infrastructure or improving education.

 At the heart of the problem is the immense distance between the EU and the electorate. James Tilley, of Jesus College, Oxford, has argued, when a European country gets frustrated with its rulers it can kick them out at election time; but when they become frustrated with Europe there is no one to kick but the institution itself. For countries that benefit from EU funds, there are tangible reasons to be forgiving; but for countries such as Britain that see Brussels as a cost, that psychological buffer is not there.

 So we are left having a referendum where the “out” campaign has a strong populist card to play; while the “in” campaign has a highly contingent argument to make about the economy. If Greece settles down, the eurozone returns to solid growth and the trade benefits become obvious, they stand in good stead. But if the EU becomes a byword for economic chaos, patronising elites and unfettered immigration, then whatever renegotiation Mr Cameron manages to deliver in Brussels is unlikely to be enough.