Counties in the East are being targeted by exploitative drug traffickers, with hundreds of gang members infiltrating rural areas.
Norfolk is the worst affected, according to a report from City Hall, the Mayor of London's office.
It claims there are 416 individuals with links to county lines gangs in the county, and 167 of them are in Norwich; that figure makes it the worst place in the country for drug trafficking activity.
County lines refers to the movement of drugs and other illegal goods from London to rural areas.
Number of individuals with links to county lines gangs in the Anglia region:
Thames Valley: 251
(Source: City Hall)
The gangs typically use young people to move illicit goods, which can include weapons and money as well as drugs.
The report says they are recruited at their most vulnerable, having gone through situations like school exclusion or family breakdown.
The role of public transport in moving young people with illegal goods around the country has also been highlighted.
The report says: "Networks are believed to be exploiting their local train links.
"[Gangs use] National Express buses, particularly from Victoria Coach Station and London airports. National Express tickets are cheaper than train travel, particularly with a child ticket."