LONDON - Britain is revving up for one of the tightest and most unpredictable elections in memory, as Prime Minister David Cameron fights to retain power and call a referendum on European Union membership.
A fragmented vote yielding a new coalition is seen as the most likely outcome, thrusting smaller parties into the limelight in a country that is still used to a traditional split between Conservatives and Labour.
The campaign so far has been dominated by the rise of the anti-EU UK Independence Party (UKIP), and peppered with debate on immigration, health spending and economic wellbeing during a recovery following years of austerity.
If Cameron's Conservatives win outright on May 7, the premier has said he will seek to renegotiate Britain's relationship with the EU before calling an in-or-out referendum on membership by the end of 2017.
But as the 100-day countdown to elections begins Tuesday, experts predict that neither the Conservatives nor Labour will secure a majority in the 650-seat House of Commons.
Instead Britain could face days of uncertainty - with some experts even warning that the result may be so unclear that new elections will have to be held.
"The only prediction is that it's incredibly unlikely that any of the main parties will end up with an overall majority," Professor Tim Bale, chair in politics at Queen Mary, University of London, told AFP while stressing that neither he nor anyone else could credibly forecast the outcome now.
Anti-EU UKIP surges
For the past five years, the Conservatives have governed with the centrist Liberal Democrats in Britain's first coalition government since World War II.
Opinion polls put the Conservatives and centre-left Labour almost neck-and-neck.
The Conservatives receive 32 per cent voter support versus 33 per cent for Labour, according to an average of leading surveys calculated by the UK Polling Report website.
Nigel Farage's UKIP is ranked third with 15 per cent, while Cameron's coalition partner Liberal Democrats have plunged to eight per cent, just ahead of the Greens' seven per cent.
The Scottish National Party (SNP), which wants independence for Scotland but lost last year's referendum on the issue, is also set to make major gains. It is thought to be targeting between 12 and 20 seats, up from six at the moment.
Cameron is campaigning on the economy, telling voters that they cannot afford to jeopardise Britain's recovery - the strongest among major European nations - by ditching the Conservatives.
However, the Conservatives have struggled to shake off their "nasty party" label, with many voters believing austerity measures have slashed public services such as the cherished National Health Service (NHS) too harshly.
Labour says its economic plan would prove less damaging to the NHS and other public services, while cutting a £91.3 billion (S$185 million) deficit.
But its leader Ed Miliband is dogged by questions about his leadership skills and a socially awkward public image.
Last year, he was photographed eating a bacon sandwich clumsily, and a one-time colleague this month described him as a "patronising" oddball.
With experts predicting that neither main party will be able to rule on its own, Cameron or Miliband will likely have to find allies.
This could either materialise in a formal coalition, or on an informal basis where parties back a minority government on key votes in return for policy concessions.
The Liberal Democrats and the SNP look best placed to win enough seats to durably prop up a government.
"There's a pretty sizeable chance of a scenario where Labour wins the most seats, doesn't have a majority, but can get through a functioning governing majority with either the Liberal Democrats or the SNP," elections expert Benjamin Lauderdale of the London School of Economics told AFP.
Though support for the Liberal Democrats' has dropped by over two-thirds since 2010, the party could retain up to 30 seats, according to Bail, down from 56 currently.
Parties like UKIP may not win as many seats as their support in polls suggests, because under Britain's first-past-the-post system, it is only the ability to win individual seats that counts - not a party's nationwide level of backing.
Professor Steven Fielding of Nottingham University predicted that UKIP could win "a handful of seats, probably five to 10" in the House of Commons.
"I don't think this election will see UKIP gaining a lot of seats, but it may give them sufficient influence to ensure a referendum," he told AFP.