LONDON (Reuters) - A British anti-EU party has polled more votes than the ruling Conservatives in two elections for parliamentary seats, in the latest sign that Prime Minister David Cameron's party faces a threat from the right.
The UK Independence Party, or UKIP, is enjoying a surge in popularity as some right-leaning voters become disillusioned with the ruling Conservative-Liberal Democrat coalition against a backdrop of persistent economic problems.
Results showed on Friday that, as expected, the main opposition Labour Party had comfortably won the three seats, Croydon North, Middlesbrough and Rotherham, that were up for grabs in by-elections on Thursday.
But the more striking result was that UKIP came second in both Rotherham and Middlesbrough, while the two coalition parties suffered a drubbing.
"Our previous best-ever by-election result, a fortnight ago, was 14.3 percent and this one is comfortably over 20 percent," UKIP leader Nigel Farage told the BBC in Rotherham in the early hours, after the results were announced.
"Whichever way you look at it, UKIP is on the rise."
The Conservatives came fifth in Rotherham, after Labour, UKIP, the far-right BNP and the far-left Respect. The Liberal Democrats came an embarrassing eighth, behind a local clergyman running as an independent candidate.
UKIP had enjoyed a boost in support during the Rotherham by-election campaign after the Labour-run local council caused an uproar by removing children from a UKIP-supporting foster family.
The council said it took the step because the children were from an EU migrant background while UKIP had long taken a very hostile position towards the European Union, but politicians from across the spectrum condemned the council's decision.
The scandal may have contributed to UKIP's strong showing in the Rotherham by-election, but results elsewhere suggested support for UKIP was broadly on the rise.
In Middlesbrough in northeastern England, UKIP came second, the Liberal Democrats third and the Conservatives fourth. In Croydon North, a London seat, the Conservatives came second, UKIP third and the Liberal Democrats fourth.
Britain's "first-past-the-post" electoral system makes it hard for fringe parties to win parliamentary seats as they have to beat all other parties in an individual constituency. UKIP has no presence in parliament.
But many Conservatives are worried that in the next general election in 2015, UKIP could split the right-leaning vote, making it harder for Cameron's party to win seats that are tightly contested with Labour or the Liberal Democrats.
They fear UKIP may scupper Conservative chances of winning an outright majority and forming a government alone.
(Reporting by Estelle Shirbon; editing by Andrew Roche)