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 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.
Nottingham University professor of politics Philip Cowley said: “It’s not true to say that it’s the first election which we have expected to produce a hung Parliament - but it is the first election in living memory where we expect the outcome to be as messy as it might be, with it being quite possible that a combination of the first and third placed parties will not be able to form a coalition. It’s also quite possible that we will end up with no truly ‘national’ party after the dust has settled.”
The vagaries of the UK electoral system mean Labour could win the most seats with fewer votes than Tories, while Ukip could scoop up around a fifth of national support and have only a handful of MPs to show for it. Labour could suffer a bloodbath in Scottish strongholds at the hands of an SNP which has seemed invigorated by defeat in the independence referendum.
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 eurosceptic Conservatives and Ukip could between them secure more than 50% of the vote, but the result could be a pro-EU Labour-Lib Dem coalition.
Election expert Professor Richard Rose of Strathclyde University said: “Asking which party is ahead in the public opinion polls is meaningless in this close-fought election because seats in the House of Commons are awarded at the constituency level, not the national level.”
Instead, the result could depend on the scale of Lib Dem losses, with Tories reaping most of the benefits if Nick Clegg’s party loses MPs because they are in second place in more “yellow” constituencies, he suggested.
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 usual 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 Institute for Fiscal Studies suggests could amount to a “fundamental reimagining of the role of the state”.
IFS director Paul Johnson judges the disparity between the two main parties’ economic plans to be the widest for many years, with spending cuts of at least £33 billion after 2015/16 under the Tories, compared to £7 billion with Labour, which he says has left itself leeway to borrow up to £50 billion more by 2020 at the cost of building up debt.
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 warn that Miliband would put recovery at risk with higher taxes and more borrowing.
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.
Parliament is not set to dissolve until the end of March, when party manifestos will be published and the battle-bus tours get under way. But in reality, the campaign is already in full swing, with the New Year marked by a blitz of speeches and policy announcements.
Voters can expect to hear Tory ministers intoning the words “long-term economic plan” with metronomic monotony over the coming weeks, while Labour spokesmen endlessly repeat their pledge to build “a Britain that works for you, not just the powerful few”.
Conservatives have named their six key election themes as the economy, jobs, taxes, education, housing and retirement, while Labour will take every opportunity to shift the debate onto the NHS and public services. Both may struggle to prevent Nigel Farage from dominating the headlines with his populist message on Europe and immigration.
Meanwhile, Mr Clegg will position Liberal Democrats as a restraining influence on whoever is in the best position to form a coalition after the election, offering a “stronger economy” than would be delivered by Labour governing alone and a “fairer society” than the Tories would create left to themselves.
With proposals for as many as seven parties to feature in the televised leaders’ debates expected to punctuate the campaign, 2015 is shaping up to be the first truly multi-party election, with the prospect of a patchwork parliament replacing the traditional serried ranks of blue and red.
The complexity of the likely result could mean weeks of horse-trading to forge a coalition or a “supply and confidence” agreement allowing a minority government to get its Queen’s Speech and Budget through the Commons.
Constitutional convention is that the existing PM stays in office until it becomes clear who is in a position to form a new administration, and Whitehall mandarins are now considering how best to keep the business of government going during this potentially lengthy period - and what to do if no stable government can be formed and the UK is plunged straight into a second election for the first time since 1974.
Cath Haddon, of the Institute for Government, said: “Events in May will test not only our democratic system, but also the constitutional guidance that exists around elections in this country.
“We already know what happens during an election campaign, so what we need greater clarity on is what happens between an inconclusive result and the formation of a new administration - the ‘caretaker period’.
“Government, Whitehall and Parliament should be thinking ahead now about whether the conventions for a caretaker government are clear on what role it plays and how long it should stay in government. With so much uncertainty in this election, it is important to reduce confusion in this area.”