Britons prepare to vote in election cliffhanger

Britons head to the polls on Thursday for their most unpredictable election in living memory, with fears of weeks of brinksmanship as the two major parties struggle to cobble together workable coalitions.

With no party expected to win a majority and several smaller blocs on the rise, the election could also mark a shift to a type of fragmented politics that is more familiar in other parts of Europe.

Deputy Prime Minister Nick Clegg, the leader of the centrist Liberal Democrats, has even warned of another election this year if an unstable minority government takes power.

On the final day of campaigning Wednesday, Conservative Prime Minister David Cameron and his chief Labour rival Ed Miliband embarked on frenetic tours of the country in a scramble for votes.

A Conservative victory could raise the risk of Britain exiting the European Union because it would mean a membership referendum, while some experts warn that a Labour win could spread unease among investors.

The Conservatives and Labour have sharply different views over whether to continue austerity cuts in the world's fifth-biggest economy, which have slashed the deficit but also led to widespread social pain.

At least one thing is for sure -- expected massive gains by Scottish nationalists will transform the British political scene and make the prospect of independence for Scotland a far more likely one.

Polls open at 0600 GMT and close at 2100 GMT, with exit polls published immediately after that and the first results coming in from around midnight.

Vote tallies for the 650 seats will be announced during the night and final results are not expected until Friday afternoon.

Tens of millions of people are registered to vote, and nearly 4,000 candidates are in the running for Westminster.

Ballots will be cast in around 50,000 polling stations dotted around the country, including in unusual places like pubs, caravans and even garages.

- Indecisive results -

If the election results are not decisive as widely expected, negotiations between the parties could start immediately, although they may be delayed by ceremonies for the anniversary of the end of World War II.

The latest BBC "poll of polls" average puts the Conservatives at 34 percent, followed by Labour at 33 percent, the anti-EU UK Independence Party (UKIP) at 14 percent and the Liberal Democrats, who are currently junior members in a governing coalition with the Conservatives, at just 8 percent.

But the percentage breakdown is a poor indicator of the final tally in Britain because of the first-past-the-post system, which counts the results only in individual constituencies, not the overall vote share.

Negotiations to form a government will likely be complicated, and a heated debate has broken out about the potential legitimacy of a coalition given that the party that wins the most seats may not end up governing.

Some polling experts predict that the Conservatives may end up winning more seats than Labour but fall short of an overall majority, and would then struggle to garner the support required to form a government.

Others predict a late swing towards Cameron and a better-than-expected performance by the Liberal Democrats.

The Lib Dems have left open the possibility of backing either the Conservatives or Labour, the SNP has vowed to block the Conservatives, and while UKIP is polling well, it is unlikely to win more than a handful of seats.

Clegg, the leader of the Liberal Democrats, has even mooted the possibility of a second election this year, warning "that is exactly what will happen if Ed Miliband and David Cameron put their own political interest ahead of the national interest".

The key test is whether any party "commands the confidence of the House of Commons", managing to win the support of at least a 326-seat majority.

An important deadline for any negotiations is May 27 when Queen Elizabeth II is due to deliver a speech in parliament -- traditionally drafted by the winning side in the election -- and a confidence vote follows.