Britain's election race tightened last Friday as a second television debate between party leaders failed to produce a runaway winner, increasing the chances of a hung parliament.

All eyes were on Liberal Democrat leader Nick Clegg in Thursday night's debate after his victory in a recent clash propelled his party out of their traditional third position.

He managed to fend off verbal attacks from Labour Prime Minister Gordon Brown and Conservative leader David Cameron, scoring a narrow victory after the leaders traded blows on issues including Europe and nuclear weapons.

The results from early polls were close, however, and suggested that the May 6 general election would be a closely fought three-way battle.

They increase the likelihood that the vote would produce Britain's first hung parliament - where no party has an overall majority - since 1974.

After the nervous start to the first TV debate, the gloves came off quickly in the second clash on Sky News television, which focused on foreign affairs.

Clegg faced a two-pronged attack from Brown and Cameron over his party's opposition to renewing Britain's Trident nuclear submarine programme, which he said was a relic of the Cold War.

"I say to you Nick 'get real, get real', because Iran, you are saying, might be able to have a nuclear weapon and you wouldn't take action against them," said Brown.