Politics matters. Whatever political party you support what is important is to stress why politics itself is important and why we go into politics, why we believe it matters

Tony Blair

The cross-party event was also being addressed by Prime Minister Tony Blair and Conservative leader Iain Duncan Smith.

Mr Kennedy believes that disaffection with politics among the voting public requires radical measures.

Last year's general election saw a turnout that dipped below 60%.

Blair heckled

The prime minister was the first of the three party leaders to address the 1,500 people in Westminster's Methodist Central Hall - and was briefly heckled over the UK's support for US action in Afghanistan.

Mr Blair, in his shirt sleeves for the question and answer session hit back, saying: "Talk to people in Afghanistan about the nature of the regime in that country before we took the action that we did.

"Afghanistan was a state which was basically funded through terrorism and drugs. "

Asked if Britain would continue its support for America's war on terrorism the Prime Minister replied: "Yes we will, because it's important that we continue until terrorism is defeated in all its forms across the world."

Tackled about his "presidential" style of leadership, he said critics would accuse a leader without a strong sense of direction as being weak, and one with clear priorities as being dictatorial.

Getting married

Mr Blair insisted to the meeting: "Politics matters. Whatever political party you support what is important is to stress why politics itself is important and why we go into politics, why we believe it matters."

Mr Blair had disappointed his audiences when he told them the Government had no plans to legalise cannabis: "There is a genuine worry based on evidence here and abroad about the link between soft and hard drugs and we are concerned about that."

By contrast Mr Kennedy was cheered when he gave his views on lowering the voting age and called for a fresh look at the whole question of whether cannabis should be legalised.

The Tory leader Iain Duncan-Smith insisted he was right to raise the case of Rose Addis because her families' complaints had been dismissed by the hospital and by the health secretary.

The Tory leader also said his party was looking at whether or not it would support scrapping Section 28.

Contrast with Pop Idol

He said it was important to balance the need to protect young people whilst ensuring that sections of society did not feel stigmatised.

Mr Kennedy argued: "You're allowed to marry when you're 16. You can join the army. And you can pay tax. Why shouldn't you be able to vote too?

"The worrying thing about last year's general election was how few people turned out to vote.

"Contrast that with the five million plus people who voted last weekend in the Pop Idol poll."

Attention for teens

Mr Kennedy believes that more people would become engaged in the political process if they were allowed to vote far younger.

He added that the move would make politicians pay "far more attention" to the opinions of people in their late teens.

Mr Kennedy was joined by Tony Blair and Iain Duncan Smith

"When we call for votes at 16, we're drawing on a very fundamental Liberal Democrat belief.

"We trust people to make decisions for themselves - the more responsibility you give them, the more responsible they will be."

Mr Kennedy's comments came as it emerged that new technology aimed at encouraging more people to vote was expected to be piloted in this year's May local elections.

Up to thirty schemes will be launched including voting using mobile text messages or online.