Two million Conservatives voters are set to switch to the UK Independence Party at the next election, according to a new survey of 30,000 voters. It found that one in five of the 10 million who voted Tory in 2010 are on the verge of switching to Ukip, despite the Tory leadership making efforts to hold them by adopting Ukip’s language on immigration and the EU.

The polling data, produced by the British Election Study, found that Ukip was still drawing its greatest support from ex-Conservatives. It found that Labour was set to lose half a million votes to the party, whilst the Liberal Democrats were set to lose 700,000 votes to them. The survey put Ukip on track to win 19 percent of the vote at next May’s general election, the Telegraph has reported.

Prof Geoff Evans, of Oxford University, who led the study, said: “BES data shows quite clearly that it’s the Conservative Party who need to worry most about the threat of Ukip – because those people who supported Labour have, in the main, already made the switch.”

The research shows that the northern working class demographic which Ukip targets abandoned Labour years ago, disgusted by Tony Blair’s third way agenda. Consequently, those who voted Labour in 2010 are mostly immune to Ukip’s messaging on immigration and therefore more likely to stick with Miliband’s Labour party.

The results are likely to encourage the Conservatives to issue fresh “Vote Ukip, get Labour” warnings, but Ukip points out that its vote is having a much more localised effect, turning two-way races into three-way marginals, and so making the outcome of the next election a lot less predictable.

Prime Minister David Cameron has recently made some announcements on immigration, hoping to stem the flow of voters away from his party. He had proposed a quota for European immigration, but when that idea was vetoed by German Chancellor Angela Merkel, replaced the proposal with new policies designed to limit the in-work benefits available to immigrants, making immigration a less attractive proposition.

However, this tactic is creating a backlash amongst his own team. Yesterday the Tory defence minister Anna Soubry, who sits on the left of the party, accused Cameron of stoking up false fears on immigration by pandering to Ukip.

Speaking on BBC 4’s flagship Today program, Soubry said: “I want to know and understand why my Prime Minister who I have huge amounts of respect for, I genuinely do, I think has done an outstanding job, I want to know why he’s come to that conclusion. Is that the real problem, that people might be able to claim benefits? There’s a danger that you create false fear and sometimes you play to people’s prejudices.

“It’s really important that we make it clear that the majority of people who come to our country come here to work these are good people. Just because some people have a particular view, doesn’t mean to say that you should pander to it.”

During the interview she also related how, after accusing Ukip’s leader Nigel Farage of talking “prejudice” on the BBC’s Question Time, she had been called by both David Cameron and Labour leader Ed Miliband who congratulated her on her comments, which they said they agreed with.