Tony Blair is due to host a gun crime summit at Downing Street, following a recent spate of fatal shootings.
Teenager Billy Cox was found dying at the family home by his sister
The prime minister and Home Secretary John Reid are expected to meet police, council leaders and community workers.
Conservative leader David Cameron, who is visiting a community project in Manchester, questioned if the summit would "get to grips with the issue".
Five people have been shot dead in London during the last month - three of them teenagers.
The government is planning to push through new laws making it an offence for an adult to pass a weapon to a younger sibling or friend.
The Violent Crime Reduction Act, already approved by Parliament, was due to come into effect at the end of the year - but ministers want it to be implemented in April.
Passing a weapon on will now draw the same punishment as possession of a weapon.
Mr Blair has suggested the minimum age at which someone faces a mandatory five-year jail sentence for possessing a gun could be reduced from 21 to 17.
And the prime minister has told the BBC he is considering criminalising gang membership.
The number of people injured by firearms in England and Wales has more than doubled since 1998
In 2005/2006, the number of gun murders fell by more than a third from 78 to 50
There were 11,084 recorded firearms crimes in 2005/2006 - up 0.12% on previous year
London, Greater Manchester and the West Midlands account for 54% of recorded incidents
Source: Home Office
Mr Cameron said he hoped the summit was real, and not just a photograph opportunity.
He suggested a recent cancer summit held at Downing Street had yielded little.
"Tony Blair welcomed everyone, shook their hands, had his photograph taken. Half an hour later he had gone.
"Now, let's hope [the gun crime summit] is a proper summit. That they do get to grips with the issues."
Mr Cameron has argued that a lack of role models was fuelling gang culture and called for fathers to be compelled to take a greater role in bringing up their children.
He supports the idea of tax breaks to help families stay together and promoting a "culture of responsibility and respecting authority".
'No quick fixes'
But Mr Reid, who visited south London on Wednesday, ridiculed Mr Cameron's stance on crime, saying the problem would not be solved by "hugs and kisses".
"We'll need understanding and public protection measures and if that means more police and punishment in the meantime then it has to be part of the solution."
Lib Dem leader Sir Menzies Campbell said there were "no quick fixes" to the problem.
Criminal justice charity Nacro said the summit was a "unique opportunity" to listen to the "consistent messages" coming from front-line community workers.
Nacro boss Paul Cavadino said "simplistic measures" like five-year minimum jail terms would not help to reduce gun crime - instead, officials should concentrate on educating young people.
"We need to combat the idea that you are safer carrying a firearm by putting across the strong message that if you live by the gun, you are more likely to die by the gun."
There have been five fatal shootings in London in the past month, three of which were of teenagers in the south of the city - two of them killed in their own homes.
A 28-year-old man was shot dead in Hackney, east London.
Christian leaders are organising a "prayer walk" through the two London boroughs blighted by recent killings - Southwark and Lambeth.
They say the walk, to take place at dusk on Thursday, will demonstrate the "total abhorrence of the vast majority of black Londoners to gun violence".
Claudia Webbe, an adviser to the police's Operation Trident unit which deals with crime in London's black community, said she wanted to see more youth workers on the streets.
"It's got to be issue-based work, it's got to be on the streets, it's got to be after hours, it's got to be at weekends," she said.