LONDON (Reuters) - Prime Minister David Cameron's Conservatives risk losing a second British parliamentary seat to the anti-EU UKIP party on Thursday, foreshadowing a possible political upheaval in next year's national election.
With distrust of mainstream parties and anxiety about immigration rising among voters across much of the country, four opinion polls have suggested UKIP (the United Kingdom Independence Party) will win Thursday's by-election in the southeast English constituency of Rochester and Strood.
Thursday's vote was called when the constituency's Conservative member of parliament Mark Reckless resigned after defecting to UKIP, which favors an immediate British withdrawal from the European Union and sharply lower immigration.
Victory for Reckless, who is seeking to regain his seat for UKIP, would deepen fears among European partners of a possible British exit from the EU. It would also deal a serious blow to Cameron who ordered his party to mobilize all its resources to hold Rochester, visiting the area five times before the ballot.
Final results of the vote, which follows a by-election last month when another Conservative defector won UKIP's first elected seat in parliament, are expected around 10 p.m. ET on Friday morning.
Success for UKIP would also deepen Conservative fears of a split right-wing vote in the election to the Westminster parliament in May 2015, making it harder for Cameron to hold onto power. This could stoke disquiet among Conservative lawmakers about his leadership, some of whom might also be tempted to defect.
"If I do win there will be a significant change in people's assumptions about UKIP," Reckless told Reuters in an interview. "People will realize that we're credible and a party that is likely to win many more seats in Westminster next year."
Reckless defected in September, saying said he had lost faith in Cameron's promise to wring serious reform from the EU if a Conservative government is re-elected.
Reckless declined to forecast if a UKIP victory would encourage more defections, but said the contest was part of a reordering of Britain's traditional two-party system.
Cameron's party and the left-leaning Labour party have taken turns to govern Britain since World War Two but their collective support is waning. Cameron was forced into a coalition with the center-left Liberal Democrats after failing to win an outright majority four years ago.
At least one opinion poll has since suggested that combined voter support for the two main parties has dipped below 60 percent for the first time since then.
At the same time, UKIP, broadly to the right of the Conservative party, and the Scottish National Party (SNP), broadly to the left of the Labour party, have exploited voters' disenchantment to siphon off support from both.
Cameron's party narrowly trails Labour in opinion polls but neither looks likely to win outright, raising the prospect of another coalition or a power-sharing deal with a smaller party.
Cameron once described UKIP as "closet racists" but apart from poaching two of his lawmakers, it also won European elections in the United Kingdom in May.
He tried to neutralize UKIP by promising to renegotiate Britain's EU ties before holding a referendum on membership in 2017. But he has not so far spelt out exactly what changes he wants or forged strong alliances with EU partners to win them.
His strategy has alarmed some EU allies, particularly his talk of wanting to find a way to curb European immigration to Britain. "We are talking with Britain and I love Britain and want to keep talking to them," Gunther Krichbaum, president of the German Bundestag's EU affairs committee, told Reuters.
"But when the rhetoric is driving you at 100 miles per hour up a blind alley, you have to realize that you won't be able to turn round at the end of the blind alley," said Krichbaum, a member of Chancellor Angela Merkel's Christian Democrats.
UKIP has used soaring public concern about immigration, particularly from eastern Europe, to argue that Britain can control its borders only by leaving the bloc.
Cameron's party promised to cut net migration to the tens of thousands by next year's election, but it rose to 243,000 in the year to March 2014.
"Cameron is a liar," said Keith Marden, a retired construction worker in Strood who plans to vote UKIP. "He can't do anything on Europe."
Marden backed UKIP's plan for an Australian-style points system to select skilled immigrants and thought it should be harder for foreigners to benefit from Britain's welfare system.
Opinion polls have given UKIP a lead of up to 13 percentage points in the constituency, which is about 50 km (30 miles) from London. It is regarded as a reasonable bellwether for British politics since parts of it were once controlled by Labour before the Conservatives took it in 2010.
The area embraces Rochester's ancient cathedral, its 12th century castle, and its picturesque high street where many shops and bars are named after characters created by 19th century writer Charles Dickens who lived nearby.
Additional reporting by Stephen Brown in Berlin; Editing by Guy Faulconbridge and David Stamp