By Kylie MacLellan
LONDON (Reuters) - The UK Independence Party (UKIP) is set to come third behind Prime Minister David Cameron's ruling Conservatives in European elections, a poll showed on Tuesday, suggesting support for the anti-European Union party could be waning.
Previous opinion polls have shown UKIP, which has enjoyed a surge in support due to public concern over immigration from eastern EU members Romania and Bulgaria, coming top or second, pushing Cameron's Conservatives into third place for the first time.
But the ICM poll for Tuesday's Guardian newspaper, carried out on February 7-9, found one in five voters planned to back UKIP in May's European Parliament elections.
While that would be an increase on the 16.5 percent of the vote it took in the 2009 elections to the European Parliament, it puts them third behind both the opposition Labour party, on 35 percent, and the Conservatives, on 25 percent.
UKIP argues Britain should leave the EU to shake off stifling bureaucracy and interference in everyday life. Britain could continue to trade closely with EU neighbors but open itself increasingly to more distant markets especially in Asia.
UKIP's past success in opinion polls has produced a shift in the Conservative Party towards skepticism over the EU and a harder line on immigration.
In response to the poll, UKIP said that in previous European elections, it has gained vote share very significantly during the campaign period.
The results were adjusted for expected low turnout levels, the Guardian said, with only 27 percent of the 1,002 respondents saying they were certain to vote.
UKIP, which has never won a seat in the British parliament but has 13 seats in the European parliament, is expected to split the center-right vote at a national election in 2015.
Deputy Prime Minister Nick Clegg, leader of the junior coalition partner the Liberal Democrats, on Wednesday said political parties needed to take UKIP seriously.
"Mainstream politicians have made the mistake in the past of not taking UKIP, or the people who say they will vote for it, seriously. That time has long passed," he wrote in the i newspaper in a piece to mark 100 days until the European vote.
Appealing for the public's help in making sure Britain remains part of Europe, Clegg, whose party is set to attract just 9 percent of the vote according to Wednesday's poll, warned of the risk to the economy.
"If (UKIP) were to win this May and take Britain a further step towards self-imposed exile from Europe, it could wreck the recovery and destroy British jobs," he wrote.