JEFFREY BROWN: Now to Britain's cliffhanger election.
NewsHour correspondent Simon Marks begins our voting day coverage.
SIMON MARKS: The polls opened at dawn all over Britain, the start of what may prove to be the most exciting Election Day the country has seen in a generation. Prime Minister Gordon Brown, battling to keep his Labor Party in power, greeted reporters as he arrived to vote near his home in Scotland.
GORDON BROWN, British prime minister: Good to see you all. Have a good day.
SIMON MARKS: David Cameron, leader of the opposition Conservatives, voted near his home in Oxfordshire, buoyed by the campaign's final opinion poll. It showed his party enjoying an eight-point lead.
QUESTION: Were you making omelets this morning?
DAVID CAMERON, leader, British Conservative Party: I was. And I did break some eggs.
NICK CLEGG, leader, U.K. Liberal Democrat Party: I don't think my vote is a secret.
SIMON MARKS: And Nick Clegg, leader of the Liberal Democrats, whose strong performance in the country's televised election debates turned the campaign on its head, posed for photos after casting his ballot in Sheffield, in Northern England.
Turnout was high across the country, but among voters casting their ballots in Central London this afternoon, public opinion was still very divided.
WOMAN: The reason I really like Lib Dems is that I think that it's time we change how Parliament is run, and they're the only ones who seem very keen to do that.
MAN: I decided to go blue, Conservative, new change, and I think some of the things that they have got going in terms of policies for rejuvenation within the economy, they sound a lot better than the Labor.
WOMAN: I was a bit tempted by perhaps a new -- a new party being in power, Liberals. But, in the end, I still follow my instinct, and I prefer Labor to Liberal.
SIMON MARKS: British voters don't choose a national leader. They vote for local members of Parliament. The party that wins the largest number of seats in Parliament then forms the government.
But, in a closely-run election like this one, all sorts of outcomes are possible, including an era in which no single party enjoys a clear majority, something the country hasn't seen since 1974.
RODNEY BARKER, emeritus professor of government, London School of Economics and Political Science: Whoever is the largest party, Labor or Conservative, it's very likely that they will not have an overall majority, in which case, of course, the -- the Liberal Democrats will be in a very powerful position, because, in order to have a majority, a working majority in the House of Commons, whoever is the larger party will need Liberal Democratic support.
SIMON MARKS: The election campaign was dominated by domestic issues: the economy, the state of public services, immigration, and political reform. Foreign policy took a backseat, despite growing public concerns about Britain's role supporting U.S.-led efforts in Afghanistan.
In the televised campaign debates, the candidates sparred over the U.K.'s status as a close U.S. ally. Gordon Brown and David Cameron portray themselves as supporters of the traditional Atlantic alliance, and took issue with Nick Clegg's more Europe-centered stance.
GORDON BROWN: We need America on our side. Your anti-Americanism will not help us.
NICK CLEGG: I have a very simple attitude. It is an immensely, immensely important special relationship, but it shouldn't be a one-way street. We shouldn't always automatically do what our American friends tell us to do.
DAVID CAMERON: If I was your prime minister, I would want to think very carefully what's in the national interest, what will make us safer here in the United Kingdom. Do we have a political strategy for how we are going to get out of that country once we have tried to make it safe with our allies?
NEWS ANCHOR: It's exactly 10:00. And looking at those astonishing figures, ITV News is predicting the first hung Parliament since 1974. Our exit poll says that the Conservatives will win 307 seats, Labor 256, and the Liberal Democrats 59. Remember, you need 326 to cross that winning line.
SIMON MARKS: As the polls closed tonight, British broadcasters unveiled the results of their exit polls, which have not always proved reliable in the past.
Ballot-counting is now under way in earnest all over the country, with millions of people burning the midnight oil as they wait to see whether the result will be clear enough to allow anyone to occupy the prime minister's office, Number 10 Downing Street.