London, England (CNN) -- Full-on American-style politics came to Britain Thursday, as the leaders of the three big parties held the country's first-ever televised election debate.
British voters go to the polls in three weeks to decide whether Gordon Brown will stay on as prime minister, winning a historic fourth consecutive victory for his Labour party.
Polls give David Cameron's opposition Conservative party a narrow lead, but given the quirks in the British voting system, it may not be enough to make Cameron prime minister on May 6.
Brown -- whose personal popularity is lower than that of Cameron or Liberal Democrat party leader Nick Clegg -- came out on the attack, repeatedly demanding answers directly from Cameron.
He also got the first laugh of the night with an obviously scripted, but well-delivered jab at how he is depicted on Conservative party election posters. Even Cameron laughed good-naturedly.
A snap poll suggested that Clegg won the debate resoundingly.
Just over half of respondents to a YouGov poll said the Liberal Democrat leader performed the best in the debate. Just under a third picked Cameron, and just under one in five picked Brown.
YouGov questioned "around 1,000 viewers of the live televised debate from around Britain," the agency said.
Former British Foreign Minister Lord Douglas Hurd, a Conservative, said the Liberal Democrat had the easiest role in the debate.
"Clegg has the big advantge, he can say 'a curse on both your houses,' and that is rather effective," he said as a debate commentator for CNN. "It's an easy card to play."
Lord David Steel, one of the founders of the Liberal Democrat party, told CNN the debates could be very influential, even though British voters do not choose a prime minister directly.
"Electing your own MP is crucial," he conceded. But, he added, "There are a heck of a lot of people who don't know the candidates, who will be influenced by these debates."
An Ipsos-MORI poll this week suggested that as many as three out of of five British voters consider the debates very important in determining their choice.
Brown managed to keep smiling through much of the first half of the event, likely having been urged to avoid looking dour or gloomy, as he is often portrayed.
The camera did catch him smirking on one or two occasions, an expression for which U.S. Republican presidential candidate Sen. John McCain was lambasted during his 2008 run against Barack Obama. It's not yet clear if British voters will be as turned off by the grimaces as the American public reportedly was.
Thursday's debate was the first of three head-to-head-to-head faceoffs for the party leaders. It focused on domestic policy, and the candidates took questions on immigration, the military, law and order, corruption, the budget deficit and education, among others.
Next Thursday they clash over foreign policy, and the following week they debate the economy.
A debate between party leaders has been 50 years in the making, veteran pollster Sir Robert Worcester told CNN.
"It's usually the underdog who says let's have a debate and the (poll) leader says don't be ridiculous," he said.
"Brown is well behind and Cameron was so far ahead when he agreed to do it that he thought he had nothing to lose," said Worcester, founder of the MORI polling agency.
But Labour has narrowed the lead in the polls, and Cameron is "probably kicking himself because (the debate is) for him to lose," Worcester said.
"The British love the underdog so it may well come out tonight that Brown won the debate because his poll rating went up and Cameron lost because his didn't," Worcester predicted.
British voters go to the polls on May 6. The Labour party has been in power since 1997, when they wrested power away from the Conservatives after 17 years.
Voters will chose lawmakers in 650 districts, or constituencies, across the country. The party with the most members of parliament traditionally gets the first chance to form the government.