Voters headed for the polls across Britain Thursday, in a contest that is expected to produce an ambiguous result, a period of frantic political horse-trading and a bout of national soul-searching.

Prime Minister David Cameron's Conservatives and Ed Miliband's Labour Party are running neck and neck, and neither looks able to win a majority of Parliament's 650 seats.

Many voters are turning elsewhere — chiefly to the separatist Scottish National Party, which will dominate north of the border, and the anti-immigrant U.K. Independence Party. UKIP is third in opinion polls but Britain's electoral system means it can win at most a handful of seats.

If no party wins outright, it may take days or weeks of negotiation to forge a workable government.

Labour leader Ed Miliband cast his vote early alongside his wife, Justine, in northern England. Early voters were bemused to find photographers, reporters and television crews waiting in the middle of the briefly closed-off road in Miliband's Doncaster North constituency.

UKIP leader Nigel Farage also voted early in the southeastern constituency of South Thanet, and then tweeted: "I can't tell you who I voted for!"

In the bright early-morning sunshine in London, voters gathered to cast ballots at a polling station close to Parliament as police stood guard.

Signs of the unfolding political drama were all around. The squares opposite Parliament were packed with temporary outdoor television studios, while commuters picked up newspapers urging voters to the polls.

"It's going to be important for Britain for the next five years," said Gerry McQuillan, 61, an arts administrator voting Labour. "We're coming out of economic austerity but we've got to get the right government for the next five years."

Alexis Thomas, 34, a doctor, was mindful of all the predictions of a dead heat and wanted to make her voice heard.

"Because it's so tight, I think that if I didn't come out and vote, and didn't get the result that I wanted, then I'd only have myself to blame," Thomas said — though she wasn't saying what result that was.

Polls are open from 7 a.m. (0600 GMT) until 10 p.m. (2100 GMT).

Three issues — the economy, the National Health Service and immigration — have dominated the British election. Here's where the candidates stand on the things that matter to voters:

THE ECONOMY ABOVE ALL

The election boils down to a simple question: Did the Conservative-led government chart the right course through the aftermath of the economic crisis — the worst recession since the 1930s?

Prime Minister David Cameron has focused on headline numbers after five years of budget cuts designed to shrink the deficit and bolster growth. Inflation is down, employment is up and the economy is growing at one of the fastest rates among large industrialized nations.

The Conservatives argue they need time to cement the gains and ensure the benefits trickle down to everyone. They promise no new income or value-added taxes.

Opposition leader Ed Miliband is urging voters to look deeper, arguing the topline figures don't tell the whole story. Real wages are below pre-crisis levels, employment figures have been inflated by low-skill jobs, and rising numbers of people are turning to food banks to make ends meet. Miliband has focused the debate on inequality, saying the recovery hasn't reached working families. He's promising to increase taxes on the wealthiest members of society.

NATIONAL HEALTH SERVICE

The state-funded NHS is a source of pride in this nation of 64 million — and a source of agony for political leaders struggling to pay the ever-increasing bill.

The most sacrosanct issue in British politics, leaders spent much of the campaign making promises to save the service. Miliband, leader of the Labour Party, has promised to recruit 8,000 more doctors and 20,000 more nurses, paying the bill with a tax on properties worth more than 2 million pounds ($3 million).

The Conservatives promise to increase spending by at least 8 billion pounds by 2020 and cut down on so-called health tourism, in which migrants travel to the U.K. for medical care paid for by British taxpayers.

IMMIGRATION

Britain's growing economy has attracted thousands of migrants from the European Union, particularly from the former eastern bloc countries that have recently joined the 28-nation free-trade zone.

The influx is changing Britain and straining schools, hospitals and other public services. The U.K. Independence Party has capitalized on the outrage of unhappy Britons. The once-fringe party stands third in opinion polls after promising to leave the European Union, "take back control of our borders" and restrict immigration to skilled workers needed by the British economy.

Labour plans to ban recruitment agencies from hiring only from overseas and crack down on employers that abuse workers. The Conservatives say they will reduce migration from other EU states by making it harder for recent immigrants to claim benefits. The party says it has an "ambition" to reduce annual net migration to less than 100,000 from almost 300,000 in the 12 months through September.