David Cameron's best hope of seeing his Conservatives beat the UK Independence Party (Ukip) into third place in next year's European Parliament elections may hinge on changing the voting system so voters can choose eurosceptic Tory candidates, according to a study published today.
Under the "closed list" system used for Euro-elections in the UK, which asks voters to mark their X next to the name of their preferred party, Ukip looks set to come second behind Labour next May - with some commentators even predicting a surge into first place.
But polling carried out for the London School of Economics and the Electoral Reform Society found that Tories could turn the tables on Nigel Farage's party under the alternative "open list" system, which allows voters to choose individual candidates on a party slate.
The YouGov survey suggested that the change - which would allow eurosceptic voters to pick and choose the candidates from mainstream parties whose views best reflect their own - could be worth five points to the Conservatives, leapfrogging them past Ukip, whose support could drop by as many as six points.
Professor Simon Hix, head of the LSE's Department of Government, said the current system encourages eurosceptics to register a protest by giving their vote to Ukip.
"Our poll shows that if the voting system were changed to an open-list system, many voters would switch their support," said Prof Hix. "In particular, many eurosceptic voters would support a eurosceptic Conservative candidate rather than vote for Ukip. Under the current system, in contrast, the fact you have to vote for a party rather than an individual encourages eurosceptics to protest against the three mainstream parties."
Some 30% of British adults questioned by YouGov said they would back Labour if the European elections were held tomorrow under the closed list system, against 25% for Ukip, 23% Conservative, 12% Green and 10% Liberal Democrat.
By contrast, if the open list system was used, Labour would receive the backing of 31%, Tories 28%, Ukip 19%, Lib Dems 12% and Greens 10%.
Katie Ghose, chief executive of the Electoral Reform Society, said: "This research shows the huge effect of giving people a real choice at elections.
"Clearly, more eurosceptics would choose the Conservatives over Ukip if they could pick an actual candidate rather than the party's pre-ordained selection. If the Conservatives were to let people, rather than parties, choose their European representatives, they could do a lot better in the polls.
"There is still time to move from a closed-list to an open-list system before the 2014 election. The Conservative Party should take note. Give people more choice, and it could serve you well."
Open-list systems are used in European Parliament elections in 18 of the 28 EU nations. Unlike the rest of the UK, Northern Ireland has used the single transferable vote system, where voters rank individual candidates in order of preference.
* YouGov interviewed 8,000 people between June 26 and July 5.