Is immigration—and Nigel Farage—key to the EU No campaign?

Nigel Farage has today said that Ukip, his party, won't be joining either of the two existing campaigns to leave the EU. Instead, he says, he will work with all anti-EU groups to secure the "out" result Ukip wants in Britain's membership referendum. He told the Today programme he didn't want to lead the campaign himself and that Ukip wouldn't be pitching for a designation as the official No campaign. So his announcement seems less about applying for a job and more about getting airtime for his key argument; that the No campaign should have immigration at the heart of its message. Referring to Ukip's former head of Policy Suzanne Evans this morning, he said: "she also said that that we shouldn't major on immigration in the referendum and I just think she was wrong."

Key to Ukip's success has been its conflation of the issue of EU membership with the issue of immigration. People moving to Britain from other EU nations—difficult to control thanks to the union's "freedom of movement" rules—makes up 42 per cent of all immigration to the UK. Ukip has played off the discomfort many Britons feel about mass immigration, arguing that we can only keep net migration low if we leave the union. It's worked well for them, taking them from a fringe group concerned largely with the less salient issue of British "sovereignty" to a force snapping at the heels of the major parties. But is this really the best approach for the mainstream No campaign to take?

That's debateable. The think tank British Future estimates that only about a quarter of Britons have dyed-in-the-wool anti-immigration views. The rest couldn't necessarily be trusted to vote for an anti-immigrant platform. In a referendum election, where you need to get at least half the electorate onside, anti-immigration arguments might appeal only to a comparatively small, hardcore group. As a senior figure in one of the No campaigns puts it: "Ukip speaks to a set of people—but the No campaign must speak to a set of people who are not best persuaded by [Farage]."  There is some evidence that the rise of Ukip has actually driven support for remaining in the EU. Open Europe's Raoul Ruparel has called the simultaneous rise in support for Ukip coupled with the lack of an equivalent rise in support for Brexit the "Farage Paradox."

Then there's the Mediterranean refugee crisis. The salience of immigration as an issue for the electorate has risen as more and more images of desperate people crossing the Mediterranean or stranded in Calais fill our screens and our Facebook newsfeeds. An Ipsos Mori poll earlier this month found concern about immigration at its highest ever level. But it would be very difficult to argue that leaving the EU would stop refugees trying to come to Britain; they already face border checks at Calais, since the UK is not part of Europe's passport-free Schengen area. Pro-Europeans might say that by being in Europe, we can push for cross-continental asylum policies which best serve both our interests and those of these desperate people.

Last, Nigel Farage offers an army of Ukip members to help deliver his message, and plans to head around the country, arguing the case for Brexit in a series of large-scale town hall events. But such grassroots clout is a mixed blessing. When I've covered Farage's rallies in the past some have been dogged by protests—such as the clashes between left wingers and far-right group Britain First (not associated with Ukip) that took place outside the party's spring conference. Back then, journalists gleefully snapped away as shaven-headed bruisers yelled "smash, smash, smash the reds!" It's hardly Ukip's fault if people cause a ruckus outside of the its events, but such rough and ready images are still likely to repel cautious, moderate voters.

Farage's committed focus on immigration has taken him from a political nobody to the leader of Britain's third party by vote share. But even Ukip has recognised that immigration alone doesn't win hearts and minds—the party diversified at the election to include strong pro-NHS messages and a firm line on the deficit. Those running the No campaigns would do well to treat Farage's siren call with caution.