But the Prime Minister insisted that the killings did not represent the state of society or its young people but arose from specific problems – and he too suggested family responsibility was a factor.

The leaders spoke in the wake of the violent deaths of five people, including three teenagers, in south London in a fortnight. Mr Cameron said he had been "shocked, appalled and deeply saddened" by pictures of Billy's body being carried out of his house.

"That's what our society has now come to – teenagers shooting other teenagers in their homes at point-blank range," he said. "It is deeply depressing and this goes beyond any one policy or any one government. We need to recognise our society is badly broken and we need to make some big changes starting now."

Mr Cameron, who went on to set out more detailed proposals in a major speech, said better policing, gun control and tougher sentences were needed. "But that is not going to stop the gangs and the gun culture. What might stop the gangs and the gun culture is stronger families."

But Culture Minister David Lammy said: "I don't want to go back to a false debate between single parents and those with two parents. It is more complicated than that."

Mr Blair, speaking at a Labour youth conference in Glasgow, described the shooting of three teenagers as "horrific, shocking and tragic beyond belief".

He pledged that the Government would publish proposals but he insisted: "Let us be careful in our response. This tragedy is not a metaphor for the state of British society."

Meanwhile, Constitutional Affairs Minister Harriet Harman, MP for Peckham in south London, suggested that parents struggled to keep children out of trouble after the age of five. Speaking outside the house where Billy died, she said: "Young people have said to me today that there are always some elements who get involved in gangs."

She added that she would be lobbying Home Secretary John Reid over concerns about the availability on the internet of imitation guns which could be adapted for use.

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