URBAN drugs gangs are targeting vulnerable adults and children in rural and coastal communities.
Around half the places affected are coastal towns with high levels of unemployment, mental health issues or crime, according to a County Lines' report produced by the agency.
The majority of the rest are more affluent areas with good transport links to major cities.
The urban gangs, which deal mainly in heroin and crack cocaine, are believed to be attracted by the combination of the potential customer base and low resistance from local dealers.
The model known as county lines refers to the use of a single telephone number for ordering drugs, operated from outside the area, which becomes the group's brand.
Unlike other criminal activities where telephone numbers are changed on a regular basis, these telephone numbers are maintained and protected.
Gangs begin by taking over premises in the target town, sometimes by coercion, by using property belonging to local addicts who are paid in drugs, or by beginning a relationship with a vulnerable female.
They use common marketing tactics to get established, including introductory offers. They will then expand the workforce, recruiting local runners to deliver drugs and money.
Ian Cruxton, National Crime Agency director of organised crime, said: "County lines is one way for high level members of criminal groups to try to distance themselves from law enforcement attention.
"The NCA and police forces are determined not to let them do that.
"This particular criminal approach puts vulnerable adults and children at risk. They are in an unsafe environment, and exposed to violence and fear.
Groups often use children, because they work for little pay, are easy to control, and are less likely to be detected.
Where girls were used they sometimes also became the victims of sexual violence.
Mr Cruxton said: "Our assessment aims to help those working with vulnerable individuals to be alert to the risks. I ask all parents, teachers and other professionals who work in this sector to be vigilant.
We know that gangs target local children who are unknown to social services and in their eyes are less likely to attract police attention."
The report found that most runners are boys aged between 14 and 17 and that grooming with gifts and money to control them via a 'debt' was common.
Deputy Chief Constable Dave Thompson, who is the National Police Chiefs' Council lead on gangs, said an investigators toolkit had been developed to strengthen intelligence flows and highlight innovative disruption plans.
He added: "With forces working in close collaboration with the NCA, we can make a difference in tackling this insidious spreading of serious crime."
The government is taking action against gang and youth violence by targeting support in the areas that need it most to reduce offending and protect vulnerable young people.
Minister for Preventing Abuse and Exploitation Karen Bradley said: "We are already working with 43 local areas facing problems with gangs and youth violence."
This work included supporting a network of over 80 experts with frontline experience of dealing with gangs and drug dealing linked to organised crime and funding to support women and girls who suffered harm.
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