Britain's political leaders are clashing in a seven-way debate before a May 7 national election.

Britain's political landscape is at its most fragmented in decades. Thursday's showdown includes Prime Minister David Cameron of the Conservatives, main opposition Labour Party leader Ed Miliband and chiefs of the centrist Liberal Democrats, right-wing U.K. Independence Party, Welsh and Scottish nationalists and Greens.

They'll have two hours to sway voters, who currently look set to deny any party a parliamentary majority.

Debates can transform a campaign. In 2010, Liberal Democrat leader Nick Clegg's performance sparked a wave of "Clegg-mania" that sent poll ratings soaring. On polling day the party took a quarter of votes; Clegg became deputy prime minister.