LONDON (Reuters) - The anti-EU United Kingdom Independence Party (UKIP) will launch an attack on Britain's opposition Labour Party on Friday as it tries to build on broadening support ahead of a national vote next year.
UKIP, which wants Britain to exit the EU and to sharply curb immigration, has in the past been seen as more of an electoral threat to Prime Minister David Cameron's Conservatives in next year's national election.
But pollsters say UKIP, which won May's European elections in Britain, is also stealing traditional Labour supporters unhappy with the left-leaning party's move away from its working class roots.
UKIP leader Nigel Farage will use his speech at his party's annual conference on Friday to make "a full frontal assault on Labour's failure to represent the people for which it was founded", a spokesman for UKIP said.
UKIP said the conference, being held in the north of England on the border of Labour leader Ed Miliband's constituency, would include a pledge to protect and improve Britain's health service, traditionally one of Labour's key priorities.
Polls show UKIP is set to win its first elected seat in Britain's parliament next month, in a vote triggered by the defection of a Conservative lawmaker to the anti-EU party.
But a second vote on the same day, caused by the death of a Labour lawmaker, could also see UKIP win a seat from Miliband's opposition party.
(Reporting by Kylie MacLellan and William James; editing by Andrew Roche)