Furness Road, in Harlesden, north-west London, is an unremarkable street. It has a school, and local shops, like hundreds of other streets all over the city.

Listen to Jon Silverman's report in full

On 5 July, at about 2200 BST, a 20-year-old drug dealer called Dean Roberts was walking along Furness Road, not far from the school.

He may or may not have noticed the red sports car parked across the road. But when the two occupants approached him, he did not stand a chance.

They were each carrying Mach 10 sub-machine guns. The weapon is popularly known as "spray and pray", because it fires 1200 rounds in a minute.

Dean Roberts became the eighth black man to be shot dead in London in the last 10 weeks.

Gangsters use sophisticated and lethal weaponry

A police study into gun violence in London has found that in a two-year period, guns were fired in the capital 291 times. One hundred and fifteen of them were multiple discharges.

For the police, there is no single obvious connection.

"Drugs may or may not be a central theme to it," says Commander Andy Hayman, the head of Scotland Yard's drugs directorate.

Conservative MP David Lidington: "We should certainly look again at immigration controls"

"But I think from our enquiries, and the contact we have had with the community, we also know there are other factors - such as gaining street credibility, and gaining respect within the community - that are the prompts for these terrible crimes."

In the first six months of this year, 13 people have been murdered in London in feuds involving black gangsters.

The upsurge of violence has been attributed to the Yardies - criminals who come originally from Jamaica and who have spawned many imitators amongst black British youth.

The original Yardies are Jamaican gangsters

One response has been to extend an intelligence operation called Trident - which has successfully reduced gun crime in Brixton - to London as a whole.

Some critics say that the Met has failed to stem black on black violence because its information network is flawed.

John Brennan, a former detective sergeant, says intelligence is the key.

"For these particular criminals, it is imperative to utilise their friends, because it is a cultural thing that is very difficult to get into," he says.

Although the term Yardie comes from Jamaica, many of the perpetrators of the violence are merely wannabes - black British youth with access to weapons, expensive tastes and cunning.

Police hope poster campaigns will help members of local communities to come forward

"They dress shabbily - jeans, t-shirts and sneakers, like a ragamuffin," says Suzy, an informant who has helped the police in a number of successful operations against so-called Yardies.

"But when they go out on the town, they will dress to a T, drive their Merc, and they'll have probably �10,000 in their pocket to buy the best bottle of champagne and have the prettiest of women and the flashiest of jewellery."

How well the police understand the phenomenon is perhaps less relevant than what they are doing to tackle it.

They hope a poster campaign and a planned London-wide conference will get the support of community leaders.

Patrols by armed response vehicles have been increased, and there is a possibility of a gun amnesty to remove some of the illegally held weapons.