The players and key issues driving Britain’s elections Thursday

The long campaign that culminates in Britain’s national elections Thursday has been filled with drama.

Prime Minister David Cameron’s Conservative Party has been touting low unemployment and other economic virtues as a reason for voters to return it to power for five more years. Ed Miliband’s Labor Party has said that factors such as the Tories’ austerity policies and a less tolerant stance on immigrants means it’s time for change.

The run has become nasty at times, especially as it’s become clear that, though the Tories will probably enjoy a small edge for the 650 seats up for grabs in Parliament come Friday morning, neither of the two parties will hold an outright majority.

Labor leaders have warned voters that Cameron will “squat” at 10 Downing St. without that majority. The prime minister has fired back that a Labor-led coalition would suffer from a “massive credibility issue.”

Both sides have faced unexpected pressure: Labor has been hit hard by the Scottish National Party, which is predicted to take nearly all of Labor’s 41 seats in Scotland -- and very likely force Miliband to rely on a party that espouses separatism, unpopular in England, for any governing coalition. The Tories, meanwhile, have been feeling a pull on their right flank from the Nigel Farage-led UK Independence Party, or UKIP, a hard-line anti-immigration group.

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FOR THE RECORD

An earlier version of this post said the Labor Party has been hit hard by the Scotland National Party. Labor has been hit hard by the Scottish National Party.

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Given this drama, what are the possible scenarios for a government -- or the likelihood that one can form soon? And just what are the various factions arguing about anyway?

The Scenarios

Pollsters are nearly certain that no one party will attain the 326 House of Commons seats needed for an outright majority. Both Labor and the Conservatives will probably end up in the 30% to 35% range, with most forecasters predicting an edge of a few percentage points to the Tories.

So what happens next?

It would seem that the Tories, if they succeed in capturing the most seats in Parliament, would be in the pole position. But the reality is trickier because Labor has a wider pool of ideological allies to choose from for a coalition. That means that the Tories may have more seats but fewer potential partners, while Labor will have more potential partners but fewer seats.

Making matters murkier -- British law is vague on what constitutes a governing coalition, saying only that an election’s winner is the party that can “command the confidence of the House of Commons.”

Although hypothetically there are more than a dozen possibilities that can unfold from there, a few are more likely than most. They break down as follows.

A coalition anchored by the Conservatives and the Liberal Democrats. Nick Clegg’s Liberal Democrats, currently in alliance with the Tories, have been circumspect about which party it will join -- and divergence on issues such as European Union membership (the Lib Dems are more enthusiastic about staying) could prove a wedge. Still, this is a simpler scenario. If the two win a combined 326 seats -- a possible though not terribly likely scenario -- and can find a way to renew their bargain, the coalition of the last five years would be returned to power.

The Conservatives and UKIP. An even less likely situation, given that Farage’s party is fading fast. Also, a Tory government dependent on a hard-line party is something Cameron and much of the leadership would like to avoid.

The Conservatives, Lib Dems and UKIP. Mathematically the most plausible, but a broad coalition of this kind can be hard to negotiate and even harder to maintain.

Labor and the SNP. A victory for the Scottish party if it happens, because SNP leader Nicola Sturgeon has made it clear she wants to govern with Labor. But even if the two wind up with 326 seats, Miliband will tread carefully -- such an alliance would get hammered by the right. He’s also said during the campaign that he won’t set up a formal coalition with the SNP. That’s in part a political calculus because he doesn’t want to alienate unionist voters. Still, the move would be very thorny, and one Labor would like to avoid.

Labor and the Lib Dems. If the two do the improbable and combine for enough seats to crack the 326 mark on their own, expect Miliband to woo Clegg hard. The Labor leader will avoid the controversial situation of becoming bedfellows with Scottish separatists. As to whether the Lib Dems would go for it, the position would be a reversal of the last five years, but the party does stand with Labor on social and other issues. Again, though, this is mathematically improbable.

Labor, the Lib Dems and SNP. There’s a good chance this would put Labor over the top, but it would be almost as hard to negotiate as the Tories’ own tripartite coalition, and would still open up Miliband to unionist and right-wing bludgeoning.

And the timeline for all this?

If neither party can form a coalition, the next big date is May 27. That’s when Cameron, assuming he chooses to stay in power in such a situation, would deliver the platform address known as the “Queen’s Speech” and then become subject to a confidence vote from Parliament several days later.

That vote, subject to plenty of backroom jockeying, will serve as a determinant of sorts, keeping the Tories in power if Cameron wins or putting Labor temporarily in his place if he doesn’t. If Labor can’t form a coalition either, it’s possible a second public election could be called, starting the process all over again.

The Issues

Party leaders have gone to great lengths to let the British public know the stakes are high, especially on domestic issues. Cameron has repeatedly said the choice is “stark.” Miliband on Wednesday said, “This is the clearest choice that has been put before the British public for a generation.”

Where are the differences greatest?

Immigration. The Conservatives have vowed to keep down annual net migration to the tens of thousands and says EU migrants will have to wait four years before they can claim benefits or social housing. They also say migrants will be unable to claim out-of-work benefits or benefits for their children if the dependents live outside the United Kingdom.

Labor plans to add 1,000 new border staff and exit checks and put a cap on the number of workers from outside the U.K. Miliband’s manifesto pledges to make it illegal for employers to undercut British workers by exploiting migrant labor, and plans to make EU migrants wait two years before they can claim out-of-work benefits.

Austerity. The last five years of a Conservative-led coalition government has seen significant cuts in public spending to reduce the budget deficit. Miliband says they’ve been draconian and hurt the lower class. Cameron argues he inherited a mismanaged budget from his Labor predecessor and such cuts have been needed.

With the budget deficit still large, both parties are driving forward with austerity. The Conservative manifesto outlines a plan to impose further spending cuts while reducing taxation. The Laborites also vow to balance the books by cutting the deficit annually, but have not outlined how much they intend to cut each year and say their government will achieve their goal through several key tax increases, also unspecified.

Healthcare. Britain’s National Health Service is seen as a drain on the nation’s purse, and the Cameron-led government has already introduced a raft of controversial efficiency savings.

The prime minister says the Conservatives will increase spending on the health service in England by at least $12 billion above inflation for the next five years. Labor has promised a $3.8-billion annual spending increase through a “mansion tax” on properties worth more than $3 million, a clampdown on tax avoidance by hedge funds and a levy on tobacco companies.

The EU. The perpetual question of Britain’s relationship to Europe would see clear consequences depending on who’s in power. Cameron has said he wants a so-called in/out referendum on EU membership in 2017 unless rules with the economic bloc are renegotiated. Miliband has said that he doesn’t think Britain should go anywhere.

We’ll find out where a lot of politicians are going over the next few days -- or weeks.

Boyle is a special correspondent.

Twitter: @ZeitchikLAT