Hundreds of drug-dealing communication lines used by gangs who often exploit vulnerable young people have been detected across the UK.

Data from Police Scotland has been used to compile what is believed to be the fullest picture yet of the threat from dealers, mainly supplying heroin and crack cocaine, it is estimated there are at least 720 so-called county lines in existence.

This specific criminal approach involves city gangs using a phone line to facilitate the supply of class A drugs into county or coastal towns.

The National Crime Agency (NCA) found almost three quarters of forces noted exploitation of vulnerable people, while nearly all forces that reported county lines activity mentioned the people involved carrying weapons.

The report is the first to include data from every police force in England and Wales, as well as Police Scotland and British Transport Police.

Young people are often groomed by gangs using alcohol and drugs and with the promise of status and wealth, according to The Children's Society.

It has called for better education around such risks.

The charity's chief executive Matthew Reed said while the report sheds light on the "shocking scale" of the grooming and exploitation of children by criminal gangs the figures revealed could be just the tip of the iceberg.

He added: "The stories we have heard from young victims of 'county lines' exploitation are horrifying and absolutely heartbreaking.

"The coercion of children into drug dealing is traumatic and puts them at great risk - they are often forced to carry drugs inside their bodies, and sent across the country to stay in 'trap houses' and sell drugs to dangerous adults."

Lawrence Gibbons, the NCA's head of drugs threat and intelligence, said: "Effective collaboration between law enforcement and safeguarding organisations must remain a vital part of the national response."

Duncan Ball, National Police Chief's Council (NPCC) lead on county lines said the report "highlights the extent of this activity across the country".

He added: "We've already been conducting operations across policing to tackle the violence associated with these lines and perhaps more significantly the real harm through the criminal exploitation of young people by organised gangs and groups."