UK faces unique general election
When MPs leave Westminster on Thursday, they will be firing the starting pistol on a general election which is shaping up to be unlike any other in recent history.
Experts are uncertain not only about which party is likely to come out with most seats on May 7, but even about whether a viable coalition assembling the magical total of 326 MPs needed for a majority will be there to be formed.
The failure of either of the two big parties to establish any kind of a lead, the polling collapse of the Liberal Democrats and the surge in support for Ukip, the Scottish National Party and the Greens have combined to make the 2015 poll less of a two-horse race to the winning line and more like a kind of random government generator.
A continuation of the Tory-Lib Dem coalition? A Labour-Lib Dem pact? An arrangement between Conservatives, Ukip and Ulster MPs? A deal under which a minority Labour administration survives with support from Scottish and Welsh nationalists, Liberals or Greens on a vote-by-vote basis? None of these is too far-fetched to be contemplated. Some more fanciful Westminster brains have even speculated over a Tory-Labour "grand coalition", which may stretch the bounds of credibility a touch too far.
What does seem far-fetched is the prospect that either David Cameron or Ed Miliband will be able to settle down in 10 Downing Street on the morning of May 8 with the confidence that a solid majority in the House of Commons will enable them to implement their manifesto in full.
And yet this uncertainty comes at a time when the result of the election matters more than is often the case.
Despite the regular moan that politicians are "all the same", the 2015 election presents voters with a change from the familiar fight for the centre-ground.
While Mr Miliband promises to take on the forces of "predatory" capitalism, Chancellor George Osborne has set out plans for spending cuts which the independent Office for Budget Responsibility suggested could put public services on a "roller-coaster" ride, with a £40 billion squeeze over three years before austerity ends in 2019/20.
Labour accuses the Conservatives of planning to take public spending as a proportion of GDP back to levels last seen in the 1930s while offering £7 billion of unfunded tax cuts to middle-income households, while Tories insist that their planned spending is actually comparable with the New Labour administration of 2000 and accuse Miliband of putting recovery at risk with higher taxes and more borrowing. The Resolution Foundation thinktank has put the gap between the fiscal plans of the two main parties at a massive £31 billion by the end of the next Parliament.
And of course, the result in May will determine whether Britain takes the momentous step of voting on its future membership of the European Union, with Tories promising an in/out referendum in 2017 whose result would have consequences for generations to come.
Labour have ruled out a formal coalition with the Scottish Nationalists, and Lib Dems have done the same with regard to Ukip. The SNP, Plaid Cymru and Greens say they will not prop up the Tories. But much will depend on the precise distribution of the 650 seats in the new House of Commons, which will themselves be decided not by a neat national swing between blue and red but by a complex technicolour arithmetic of voters switching between multiple parties in different ways in each constituency.
As they do so, confusion will be deepened by dire warnings from Labour that a vote for the SNP will help elect David Cameron, while Tories caution wavering supporters that they may "vote Ukip, get Miliband".
"In some ways, we will be facing 650 separate by-elections in this contest, because the tactical scenario is going to be dramatically different in every seat," said political history expert Matt Cole, teaching fellow at Birmingham University. "In a large number of seats Ukip threaten to drain the vote of the Conservatives principally, but also of other parties. In 18 to 20 seats, the Greens threaten to drain votes from Labour enough to make the difference between victory and defeat. "
After months bumping around in the low 30s in the polls, it would take a "remarkable turnaround" for either of the main parties to achieve the vote share - around 40% for Tories and 36% for Labour - necessary to deliver an absolute majority, said Dr Cole.
Once the votes are in, the main question will be "can a government be formed by two parties, because it is unlikely to be formable by one," he added. "If we don't have a two-party arrangement that can be made to work, we will be entering a very new arrangement - an Italian or Israeli scenario with multiple parties having to strike some sort of arrangement."
The vagaries of the UK electoral system mean Labour could win the most seats with fewer votes than Tories, while Ukip could approach a fifth of national support and have only a handful of MPs to show for it. The SNP could put dozens of Labour and Lib Dem MPs to the sword in former strongholds north of the border and become the third party at Westminster on a national vote share far short of that obtained by Nigel Farage's "people's army".
For once, first-past-the-post favours the Lib Dems, who could become kingmakers even if they trail in fifth in the polls, thanks to the incumbency factor which seems to favour their sitting MPs. It is quite possible that the electorate could entrust a total of more than 50% of votes to eurosceptic Conservatives and Ukip, only to find the outcome is a pro-EU Labour-Lib Dem coalition.
Professor Matthew Flinders of Sheffield University's Sir Bernard Crick Centre for the Public Understanding of Politics said that a result which fails to reflect the public mood could trigger a "volcano" of dissatisfaction over the functioning of British democracy.
"A major potential issue is a resurgence of a very high-profile debate around electoral reform," said Prof Flinders.
"We have got an increasingly fluid post-tribal electorate and a first-past-the-post electoral system built for a simple two-party society. If smaller parties do well in vote share, but that is not reflected in seats, reform will no longer be an issue just for constitutional anoraks and the Westminster elite, but will develop into a much broader issue around fairness."
Prof Flinders said it was still possible that voters who have flirted with minority parties in opinion polls will slip back in the privacy of the polling booth into the arms of the mainstream party which they think represents their economic interests.
But he said that each successive election was exposing the big parties' failure to adapt to the less predictable political landscape of modern society: "It's like a volcano building up and you can see the cracks and faultlines appearing. At some point the political pressure is going suddenly to burst through."