Lack of hope and parental guidance is leading teenagers to put membership of a gang above the norms of society, a leading black police officer has said.
Recent shootings in south London have prompted fresh proposals
Hackney-based Superintendent Leroy Logan told MPs that teenagers drawn to gangs needed positive role models.
A Commons committee looking at the involvement of young black people in crime also heard it has never been easier to get hold of guns.
The cost of hiring a weapon is said to have fallen to between £50 and £100.
Superintendent Logan, who gave those figures, said: "It's not only about enforcement, it's about prevent and deter.
"It's about working with voluntarily services - those positive role models - and youth services workers on a regular basis."
The committee also addressed government proposals to make gang membership an aggravating factor in sentencing.
Scotland Yard's Deputy Assistant Commissioner Cressida Dick said the public perception of gangs was "extremely exaggerated" and any legislation would be difficult to draw up.
But it might be helpful with a "small number" of gangs who do appear to be influenced by the more organised structure of US gangs.
The officer told MPs: "We are seeing some groups that are becoming more structured, that are beginning to take on the ways of operating of some of the gangs they are observing on the internet from across the ocean."
The deputy assistant commissioner also told the committee there was evidence that about 60% of people convicted of carrying a firearms are not receiving the five-year mandatory prison term introduced in 2003.
Recent shootings involving teenage victims in south London have prompted government plans to include 18-21 year-olds in the same sentencing guidelines.
Deputy assistant commissioner Dick said the minimum term did appear to have a deterrent effect and she expected its extension would also have an impact.
But she said judges were finding there were "exceptional" reasons not to pass the sentence in the majority of cases.
'Talk on streets'
She told MPs: "It isn't being applied in all cases. In fact, it isn't being applied in about 60% of cases.
"I'm sure in lots of individual cases there are very good reasons and the legislation gives indications to judges the kind of things they can look at."
Deputy assistant commissioner Dick said gun crime in London has been falling and "anecdotally" the harsher sentences appeared to be having a deterrent effect.
She added: "It's not going to have a huge one overnight - but there certainly is talk on the streets, there certainly is talk from intelligence sources that people are aware."