Britain is facing its closest election in decades and the prospect of no single party winning an overall majority. (Reuters)

About 30 million British citizens will venture out on Thursday to crumbling town halls and soaring medieval churches, set stubby pencils to paper and take part in a hallowed ritual: They will vote.

But for all the orderliness and timeless quality of Election Day, politics in Britain has rarely been as fractured as it is today. The two-party system that dominated the 20th century has collapsed, and no one quite knows what will replace it.

For a country as old as Britain, this spring’s campaign has laid bare a set of existential questions: Is it one nation or four? Is it part of Europe or not? Is it the foremost U.S. ally, or just another middling Western power?

None of those questions will be on the ballot. But the answers will be profoundly shaped by the choices voters make.

The fissures in British politics have been amply evident on the campaign trail, where the competition is no longer just between the long-dominant Conservative and Labor parties. Both are now fighting multi-front wars against challengers on the right and left. If once they were considered fringe players, these smaller parties are now central actors, with the potential to play an instrumental role in dictating the country’s direction.

Labor Party leader Ed Miliband addresses backers at a Citizens UK election assembly in London on May 4. Miliband will face Cameron in Thursday’s election. (Peter Nicholls/Reuters)

Although the Labor and Conservative parties probably will still sweep up about two-thirds of the vote, the passion and the growth clearly lie with the insurgents. These other parties are poles apart on many specific issues, but through appeals to nationalism and a shared contempt for the London establishment, they have tapped into a widespread sense of grievance across the political spectrum.

The extent of Britain’s fragmentation probably will become even starker Friday, when politicians attempt to make sense of the electoral verdict. Either Tory incumbent David Cameron or Labor challenger Ed Miliband will almost certainly emerge as prime minister. But neither has any realistic hope of securing a majority for his party. Forming a government will mean cultivating support among smaller parties that the politicians have spent years belittling.

“Whoever wins will not have a clear mandate,” said Peter Riddell, director of the London-based Institute for Government. “It will be very halfhearted.”

Britain’s deepening cleavage along nationalist lines has been perhaps the most dramatic feature of the campaign. Only eight months after Scots decisively rejected independence, they are expected to deliver a resounding victory to the Scottish National Party (SNP), which continues to champion the country’s partition.

The predicted triumph will come at a deep cost to Labor, which has dominated Scottish politics for decades. The surge by the SNP has happened with stunning swiftness, catching the political establishment by surprise. Projections show that, on Thursday, the SNP could virtually wipe out the Labor Party in Scotland. The loss of that many seats would leave Labor well short of an overall majority and could put the left-leaning SNP in a kingmaker role.

British Prime Minister David Cameron speaks to supporters during a campaign stop at Hayesfield Girls School on May 4 in Bath, southwest England. (Dan Kitwood/AFP/Getty Images)

The fires of English nationalism also have been stoked in this campaign. The U.K. Independence Party (UKIP), which has ridden the issue of immigration to prominence, is almost certain to win its highest-ever share of the vote with a message that plays in part on resentment among English citizens toward the Scots for receiving what is considered a disproportionate share of government services.

If UKIP backers take umbrage at the Scots, they loathe continental Europe. UKIP has pressed relentlessly for Britain to exit the European Union, arguing that membership is at the root of the country’s struggles with immigration.

Party backers could get their wish if Cameron makes good on a promise to hold a referendum on the European Union by 2017 should he win reelection. Such a referendum could further splinter the Conservatives, offering no good scenario for party leaders on how to wage such a campaign without potentially empowering UKIP even more.

Owing to the rise of the SNP, UKIP and the Green Party, this year’s campaign has turned on its head long-standing assumptions of how elections are won. “The truth is this is not an election that is going to be won in the center ground of British politics,” John Curtice, a professor of politics at the University of Strathclyde, said at a recent election forum in London.

Throughout the campaign, Liberal Democrat leader Nick Clegg has called on voters to turn away from the politics of “grievance” offered by the extremes, and come back to the middle. But the appeals have done little to boost the Liberal Democrats’ dismal prospects. Once the undisputed alternative to the two main parties, they are on course to lose about half their 56 seats in the 650-member Parliament.

Shifting toward fringe

The breakup of a system dominated by two main parties has been a long time coming, but it was masked by the ability of either the Conservatives or Labor to command significant majorities in the 1980s, 1990s and into the first part of this century.

Tim Bale, the chairman in politics at Queen Mary University of London, said the big change from past elections is that more people are willing “to vote with their hearts rather than vote for a mainstream party that approximates their views.”

The shift in British politics toward the political fringe is reflected in polls showing that the two main parties, along with the centrist Liberal Democrats, are on course to win their lowest ever vote share, falling from nearly 90 percent five years ago to just three-quarters today.

“The long-term issue is, this is a dysfunctional electoral system,” Riddell said. “We have an electoral system that was designed to produce single-party majority governments, which it’s failing to do.”

Thursday’s balloting will do little to settle the issues at the heart of the campaign. Instead, it will make them more acute. In pre-election analysis, various dire scenarios for the future of the country have been discussed, including whether Britain will remain united a decade or two from now.

Peter Kellner, president of the polling firm YouGov, said he worries about where the political debates could lead. Noting that there has been a centuries-long debate over the shape and makeup of what is now the United Kingdom, he said, “I don’t worry about the argument. I worry about the outcome.”

When the 2010 election produced a hung Parliament and a coalition government for the first time in more than half a century, it was seen as possibly just an aberration. That’s no longer the case. “For the foreseeable future, unless one of the two long-established major parties for some reason pulls way ahead of its rivals, we are in for a sustained period of minority or coalition government,” said Anthony King, a professor of government at the University of Essex.

Grappling with the implications of this change will begin early Friday after the votes have been counted.

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