'I bought a sub-machinegun within 24 hours'

Derrick Bennett was able to acquire the automatic weapon after informing his street contacts he wanted one.

Less than a day later, the 20-year-old was led to a seller who offered him the gun and ammunition for £200.

Mr Bennett, whose friend was shot dead in Brixton two months ago, said: "I was physically shaking when the gangsters handed me a submachine gun.

"I was so angry I could barely speak. The bullets in my hands could have been the same bullets that they used to kill my friend."

Mr Bennett was tipped off that a gun was for sale by a local gang.

Within hours he met the seller, who showed him an automatic weapon wrapped in a carrier bag.

Mr Bennett added: "I was surprised how heavy it was. How can a child carry this, let alone pull the trigger? One day I was asking around for a handgun. A day later I was holding one in my hands."

Mr Bennett spoke to one of his friends, Lewis, who had spent time in prison. He explained why young people become involved in gun crime.

He said: "Everyone has been through it. Most of it is drugs, selling drugs, mugging people, robbing places and they save their money and buy whatever feels necessary to defend themselves."

He added: "I know a lot of people who have done it through any means necessary."

During his investigation, he was also told by one 13-year-old boy that having a gun made him feel better protected and how simple it was to get one.

Mr Bennett's quest to buy a gun is featured on the BBC1 documentary Inside Out, which is aired tomorrow evening.

In the documentary, he tells how he was compelled to show how the problem of gun crime had affected his community after his close friend Nathan Foster was shot dead.

Talented equestrian and youth worker Mr Foster, 18, was killed when a gunman opened fire on him in August after he acted as peacemaker during a row.

Mr Bennett attended his funeral two weeks ago. He is one of seven teenagers who have been shot dead on the capital's streets since January.

Between April and October gun crime in London has risen 9.3 per cent compared with the same period last year.

But shootings investigated by Operation Trident - which deals with gun crime in the black community - have dropped by 4.3 per cent over that period.

Borough Commander in Lambeth, Chief Superintendent Sharon Rowe admitted the access children had to guns was "really worrying" after hearing Mr Bennett's findings.

But she pointed out that her officers had recovered 22 firearms during their operations over the last four weeks. "We have lots of intervention programmes in place which are identifying the kids that are vulnerable, that are getting caught up in this horrendous violence," she said.

Inside Out will be broadcast on BBC1 at 7.30pm on Wednesday 7 November.