Not for a generation has the outcome of a British general election been so uncertain. Yet there are two certainties about the aftermath of the May 7 ballot: it will take many days, if not weeks, to form a government, and nobody can now predict how Britain's new government would look.
Here are the possible options:
A Labour or a Conservative majority government
The two main parties in British politics have alternated in power for over a century, and almost always with an overall parliamentary majority.
Not this time, however, for neither the ruling Conservative Party nor the opposition Labour appears likely to get at least the 326 MPs they need to dominate the 650-seat Parliament.
In reality, the magic number is 323, since some Northern Irish MPs get elected but traditionally do not vote, and the Speaker of the House of Commons holds his own seat, but also does not vote.
Yet neither party looks likely to reach that lower threshold either: current opinion polls project that the Conservatives would be lucky to have 280 to 290 MPs, with Labour slightly less than that.
So, what used to be the most likely outcome in British elections - a solid, one-party government - is now the least likely result.
A "grand coalition" between Labour and Conservatives
Although this is popular in other European countries, such as Germany where coalitions are the norm, the option is highly unlikely to even be considered in London.
Grand coalitions were only attempted in Britain during war time and, as hungry as they may be for power, the mutual hatred between the country's two biggest parties is too great to bridge.
A coalition between Conservatives and Liberal Democrats
A link-up with Britain's third- largest political party will be a continuation of the coalition which Conservative leader and current Prime Minister David Cameron has headed for the past five years.
But the snag is that the Lib-Dems, as they are colloquially known, are likely to be punished by their electorate for unpopular decisions taken while in government, and are, therefore, likely to lose a large chunk of the 57 MPs they had in the outgoing Parliament.
How many seats the Lib-Dems will lose will largely dictate their availability for a coalition.
If the Conservatives gain about 290 seats - the current upper end of their predictions - and the Lib-Dems retain around 30 seats, then the current coalition may be able to survive, perhaps with the help of a handful of MPs from the Protestant community in Northern Ireland, who tend to vote with the Conservatives.
But backbenchers in both the Conservative and Lib-Dem camps are unhappy about the tie-up, and may decide to have their say before a coalition is formed.
A Conservative minority government
If a coalition with the Lib-Dems and a few Northern Ireland MPs does not work but the Conservatives still have the highest number of MPs, Mr Cameron may insist on his moral right to remain prime minister and challenge the others to vote him down.
The key test for the government may come on May 27, when Queen Elizabeth II opens the new Parliament with a speech written for her by her government; if the government loses the vote on that speech, traditionally this required the prime minister's resignation.
But recent legislation has changed that tradition, and the only way to topple a government is by passing a specific vote of no- confidence.
Mr Cameron may bet that, although he can always be out-voted by his opponents, none would be in a hurry to pull the government down and trigger early elections, so the government can limp on for a while.
Mr Cameron may also rely indirectly on MPs from the UK Independence Party (UKIP), a movement devoted to pulling Britain out of the European Union.
But UKIP is unlikely to have more than a handful of seats, and the outcome will still be a highly unstable government, facing the constant risk of defeat from its traditional opponents and also from its own rebellious backbenchers.
A Labour coalition with the Lib-Dems
Theoretically, this makes perfect sense, partly because the Lib-Dems are actually closer in ideological terms to the centre-left Labour.
But this would be relevant only if Labour leader Ed Miliband manages to get at least 290 MPs elected on Thursday, for otherwise a coalition with the Lib-Dems will still not deliver a working majority.
A Labour-Scottish coalition
The biggest upset in these elections has been the rise of the Scottish National Party (SNP), which is dedicated to gaining Scotland's independence from the UK.
The SNP is predicted to win up to 50 out of Scotland's 59 parliamentary seats, an astonishing result for a party which had only six MPs in the outgoing Parliament.
So, a coalition with Labour would make perfect sense, and may easily cross the threshold of power.
The snag is that all of the SNP's electoral gains come at the expense of Labour, which used to control Scotland, so Labour leaders would be loath to reach a deal with the party which stands for their mortal danger.
And the SNP is not very keen to be in government either; it cherishes its image as an opponent of any government in London.
Besides, the SNP is pledged to give up Britain's nuclear weapons, a "red line" for Mr Miliband, whose party is pledged to keep Britain's nuclear capability.
Labour minority government
If Mr Miliband gets 270 seats or more and a Cameron government has been rejected by lawmakers, Mr Miliband may choose to go it alone, daring the other parties to vote him down.
That will obviate the need for a deal with the SNP, and Labour strategists privately argue that they would not have to make too many concessions to the Scots, because the SNP could not afford to bring down the government, for at least a year, especially since regional elections are scheduled in Scotland for next year, and these are now the SNP's biggest priority.
Still, a Labour minority government will be open to blackmail from the SNP on an almost daily basis, and Labour may also suffer a backlash in its heartland constituencies in north England, where resentment against the Scots is growing.
Social media makes it more easy to 'swop votes'
As Britain's political leaders contemplate having to cut deals in the aftermath of a predicted messy general election result, voters have started forming pacts of their own.
Websites allowing the electorate to "swop votes" have sprung up ahead of the nation's most closely run election in decades.
The development comes amid a political scene that is increasingly polarised between right and left and fractured to the extent that only a coalition is likely to deliver a majority.
It also illustrates the growing strain on Britain's 130-year-old first-past-the-post voting system, in which parties aim to win by gaining the most seats regardless of their share of the popular vote.
Under this system, voters supporting a party with no chance of winning in their constituency often complain that their ballot is "wasted" because it has no influence on the national result.
This has led to years of tactical voting, in which some members of the public back a candidate who is not their first choice to help prevent the seat being won by a party they dislike.
But with the advent of social media and its ability to connect countless strangers, individuals with similar values can now form one-on- one agreements that allow them to vote tactically but still ensure a ballot is cast for the party of their choice.
Ms Ali Haley, 32, wants to vote for the pro-environment Green Party but it has no hope of winning in her constituency, which is held by the ruling Conservatives.
So the jewellery maker has agreed to swop her vote with a Labour supporter she met online.
On Thursday, Ms Haley will vote Labour, which has a chance of beating the Conservatives in her area. The other woman, who lives in a Conservative safe seat, will vote for the Green Party.
This arrangement allows both women to indirectly register their support for their chosen parties while helping to keep out the Conservatives.
"The idea of vote swopping worried me at first in case whoever agrees to swop reneges on her promise," Ms Haley told The Straits Times. "But I chose to have some faith."
Trust is crucial since cameras are not allowed in polling booths so there is no way for voting partners to show each other they have voted as agreed.
To build trust, the co-founder of www.swapmyvote.uk, Mr Tom de Grunwald, encourages users to research each other online.
"You can get a pretty good idea of a person's political preferences from their Twitter page," he said.
Voting partners can also reinforce their agreement by contacting one another before and after they head to the polling station.
Mr de Grunwald said the website had helped to bring about more than 1,000 vote-swop pledges since its launch in March.
Widespread disaffection with Britain's mainstream parties and the rise of formerly niche movements such as the Scottish National Party have made Thursday's general election the most unpredictable in decades.
Pundits say it could result in a hung Parliament, another coalition government or even a second election if nobody gets enough votes to govern.
"Things could get quite chaotic," Mr de Grunwald told The Straits Times. "So it's more important than ever that votes represent the fullest will of the people."
His website aims to link supporters of seven parties from across the political spectrum.
By contrast, another site called www.voteswap.org connects only left-wing voters who back Labour or the Green Party, with the objective of minimising the number of Conservative seats won.
So far, it has amassed more than 12,000 pledges to swop votes.
The Internet has made it easier for like-minded people to coordinate their tactical voting by trading votes, said Professor John Curtice, a polling expert from the University of Strathclyde.
He said the practice is legal in Britain as long as no one is coerced or bribed to vote a certain way.
Although it is too early to say what impact vote swopping will have on the election result, Prof Curtice said there is strong evidence that tactical voting has made a difference in past polls.
In 1997, it was believed to be responsible for Labour gaining as many as 20 seats from the Conservatives.
But regardless of whether it affects Thursday's result, Prof Curtice said those who swop votes still find it "psychologically appealing".
"It means you can still say you voted for the party you support," he told The Straits Times. "It's just that you got someone else to do it for you."
This article was first published on May 5, 2015.
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