Three votes will define David Cameron’s premiership. He has won two of these: Scotland remains in the union and the Conservatives once again govern with a Commons majority. The third — on Britain’s membership of the EU — could be the toughest of all. Many of the MPs and party members gathering this weekend in Manchester are already firmly set on leaving Europe and plenty more lean in that direction. Labour’s lurch to the left under Jeremy Corbyn could embolden Tory Eurosceptics unafraid of an opposition they see as unelectable. As their defining issue rises up the agenda, UK Independence Party’s (Ukip) “people’s army” is once again on the march. Early polling suggests a tight vote, leaving the prime minister with no margin for error.

If, as is widely assumed, Cameron campaigns to remain in the EU, he may have an unlikely ally in the coming battle: Nigel Farage. The Ukip leader and his party aim to play a leading role in the campaign to leave the EU, yet my research suggests this could do serious harm to the Eurosceptic cause. I presented voters with a frequently raised Eurosceptic policy demand — greater restrictions on the free movement of migrants within the EU — and randomly varied who was making the case for this reform. Net support is very high at around +25 when the policy is associated with the Conservatives, Labour or political commentators, but drops 20 points to just +5 when associated with Ukip. I found similar drops in support when other immigration policy proposals were presented as Ukip ideas.

Ukip, this research suggests, is politically toxic: voters turn against ideas when they are associated with Nigel Farage and his party, even in policy areas such as immigration, where Ukip’s stance is popular. Other research paints a similar picture: polling by the thinktank British Future shows non-Ukip voters regard the party as extreme, divisive and excessively focused on immigration. Polling by Mori on Farage paints a similar picture — a majority of voters dislike the Ukip leader, distrust his judgement and regard him as out of touch.

Risky option

The history of referendum campaigns illustrates why this poses a problem for Eurosceptics. Public support for the “change” option in referendums tends to drop during the campaign, as voters who like the idea of change in the abstract become more worried about the costs and risks as the choice becomes concrete. Advocates of change need credible leaders who can convince voters that the risks involved are low or that the status quo is, in fact, the risky option. Last year’s Scottish independence referendum illustrates this: the Scottish National Party (SNP) were able to boost support for their cause (though not by enough ultimately to win) because they were a credible and effective governing party with popular leaders. The “out” campaign in Britain’s 1975 referendum on European Economic Community (EEC) membership were unable to win people over because its leaders — Enoch Powell and Tony Benn — were seen as extremist. Such politicians amplify voters’ concerns rather than allaying them.

It is no wonder that more mainstream Eurosceptics such as Lord Lawson have already started voicing concerns about Farage’s role in the campaign for Brexit. A starring role for Farage will make it harder for the “out” campaign to paint themselves as a safe option, yet it will also be hard to lower his profile without alienating Ukip voters and activists the “out” side also need, and there are no obvious alternative star players to take his place. All of this may give Cameron some cause to smile. It was Ukip’s surging popularity with the Eurosceptic right that forced him to concede this referendum. Now Ukip’s growing toxicity with the moderate middle may help him to win it.

— Guardian News & Media Ltd

Rob Ford is a politics lecturer at the University of Manchester and the author, with Matthew Goodwin of Revolt on the Right, a forthcoming book on Ukip and the BNP.