By Kylie MacLellan
LONDON (Reuters) - The UK Independence Party, which wants Britain to leave the European Union, is set to beat Prime Minister David Cameron's Conservatives into third place and come second itself in a vote for a parliamentary seat next week, a poll showed on Thursday.
The February 13 vote, for a seat in northern England, one of 650 in parliament's lower house, is the first big electoral test this year and will be keenly watched ahead of European Parliament elections in May and a national vote in 2015.
Opinion polls have shown that UKIP is on course to beat the Conservative Party in the European elections too and to split the centre-right vote in 2015.
Thursday's poll of voters in the seat of Wythenshawe and Sale East on the outskirts of Manchester, regarded as a safe seat for the opposition Labour party, found 61 percent intended to vote Labour, 15 percent UKIP and 14 percent Conservative.
That result would represent a more than four-fold increase in the number of votes won by UKIP in the seat compared to national elections in 2010, when it finished fifth with 3.4 percent of the vote.
Labour, the holder of the seat since it was created in 1997, took 44.1 percent of the votes in 2010, giving it a majority of 7,575 over the second place Conservatives.
The vote next week was triggered by the death of the incumbent Labour member of parliament last month.
UKIP's improving share of the vote has embarrassed the Conservatives in previous mid-term votes, including in March last year when it won its biggest ever share of the vote in an election for a parliamentary seat, pushing Cameron's party into third place in Eastleigh in southern England.
Thursday's poll of 1,009 adults on February 3-5, organised by former Conservative party deputy chairman Michael Ashcroft, found 90 percent of those planning to vote UKIP were doing so to show they were unhappy with the main three parties.
(Editing by Andrew Osborn and Ralph Boulton)