Britain's anti-European Union UK Independence Party won its first elected seat in parliament on Friday by a wide margin.
In the English seaside town of Clacton-on-Sea, UKIP candidate Douglas Carswell won 21,113 votes or 60 percent of the vote, giving him a majority of 12,404.
Carswell, formerly the sitting parliamentarian from Prime Minister David Cameron's Conservative party, had triggered the by-election by defecting to UKIP.
Cameron's party came second with 8709 votes, or 25 percent of the vote. Labour came third with 3957 votes. Turnout was 51 percent, Reuters reports.
UKIP's success highlighted the threat it poses to Mr Cameron seven months before a national election and its ability to split the mainstream Conservative party's vote casting a cloud over its re-election prospects next year.
Meanwhile, Britain's opposition Labour party has narrowly retained a parliamentary seat in Heywood and Middleton in its traditional heartland in northern England, where UKIP came a close second.
The Conservatives came a distant third.