LONDON (REUTERS) - Britain's opposition Labour party narrowly retained a parliamentary seat in its traditional heartland in northern England on Friday, but the anti-EU UK Independence Party (UKIP) came a close second, notching up its best result in such a ballot.

Final results showed Labour had won the election in the seat of Heywood and Middleton in the Manchester area with 11,633 votes. UKIP came second with 11,016 votes, capturing nearly 39 per cent of the vote.

It was UKIP's best by-election result to date in terms of vote share, though it won more votes in the Eastleigh by-election last year.

The Conservatives came third with 3,496 votes, down from 12,538 in the 2010 national election. UKIP said its strong showing proved it was a threat to left-leaning Labour as well as to Prime Minister David Cameron's right-leaning Conservatives seven months before a national election.