London - Britain goes to the polls on Thursday in the closest general election for a generation - but voters may have to wait days for a new government as politicians battle to take power.
The election looks set to deliver a minority government for the first time since 1974 but could also push Britain closer to leaving the European Union and hasten Scottish independence.
Prime Minister David Cameron's centre-right Conservatives, who have led a coalition government since 2010, are fighting to stay in office but are locked in a dead heat with Ed Miliband's centre-left Labour, according to the final opinion polls before election day.
While the leaders of both main parties insist in public they can win a clear majority in the 650-seat House of Commons, they will almost certainly have to work with smaller parties to form a government.
Who will team up with whom is the biggest question of the election.
"At the moment, I have no idea who will be prime minister a month from now," Peter Kellner, president of polling company YouGov, wrote this week. "No pollster or political soothsayer can guarantee what will happen on Thursday."
Days or weeks of haggling
Millions of Britons will vote at polling stations located everywhere from shipping containers to churches and pubs between 06:00 and 21:00.
Exit polls will be released at 21:00 and most results will emerge overnight, although the final tally of seats will not become clear until Friday afternoon.
If, as expected, neither the Conservatives nor Labour win a clear majority, they will start days and possibly weeks of negotiations with smaller parties to try and build a bloc of around 326 seats.
The Scottish National Party (SNP), which wants Scotland to split from Britain, looks set to win most seats north of the border and a strong position in the talks.
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While that result would have been inconceivable a year ago, support for Nicola Sturgeon's party has soared since Scotland rejected independence in a referendum last September.
The SNP would support a minority Labour government but not a Conservative one. The party of Margaret Thatcher is deeply unpopular north of the border, where her economic reforms are still blamed for the decline of heavy industry.
Some analysts say the SNP could use its influence over a new government to push for a fresh independence referendum. Sturgeon has refused to give a date for when she wants a fresh vote.
The centrist Liberal Democrats, junior partners in Cameron's coalition government, will also have a key role to play in post-election negotiations and are open to working with either of the two main parties.
While their leader Nick Clegg is seen as closer to the Conservatives, he could struggle to hold his own seat amid expected Liberal Democrat losses across the country.
Nigel Farage's anti-EU UK Independence Party (UKIP) is only expected to win a handful of seats and therefore play a limited role in post-election negotiations.
The new government, whether led by the Conservatives or Labour, would face its first big test when lawmakers vote on its legislative programme after the Queen's Speech on May 27.
While a new government usually has to win that vote to survive, the situation could be more flexible this time if numbers are tight.
The election is being watched closely around the world due to the consequences it could have for the standing of Britain, a permanent member of the UN Security Council and nuclear-armed Nato state.
Experts say the US, with whom Britain likes to boast of a "special relationship", is already wary that defence cuts are affecting its ability to contribute to military operations as it did in Iraq and Afghanistan.
"A Little England does not augur well for a US foreign policy which aims specifically to empower like-minded states to share the burden of leadership," Jeremy Shapiro, a fellow at the Brookings Institution foreign affairs think-tank in the US, wrote this week.
Another potential issue for Britain's global status is that Cameron has promised a referendum on whether Britain, the world's fifth biggest economy, should leave the EU by 2017 if the Conservatives win.
While polling suggests Britons would currently reject a Brexit, a lengthy referendum campaign reopening the scars of the country's uneasy relationship with Europe could change that.
"This general election will determine what Britain's place will be in the world in a way that no other general election has done previously, but the importance of this is chronically under-discussed," Jeanne Park, deputy director of the Council on Foreign Relations, said last week.
The consequences of the election will start to become clear on Friday but could take far longer than that to play out in full.