Children as young as nine are being recruited by county lines gangs as they increasingly target middle class “clean skins” to run drugs, the crime chief for Britain’s biggest children’s charity has revealed.

Lynn Gradwell, head of child criminal exploitation for Barnardo's, said increased police scrutiny was forcing the gangs to change their business model and recruit children who were less likely to be suspected of crime.

“The youngest are nine or ten,” she said. “If they are out on the street after school, they are being targeted. If you think about it, when you are getting children ready for senior school, you are starting to let them walk home. You start giving them that bit of freedom.”

Barnardo’s, which has a statutory role with police to tackle child exploitation, said research from its frontline staff found 30 per cent reported an increase in gangs using “clean skins” - defined as children with no criminal record from middle class backgrounds.

Of the 38 per cent of staff that had actually dealt with at least one child being criminally exploited, almost two thirds (62 per cent) said it involved selling drugs.

Ms Gradwell cited one case of a middle class child whose parents had disciplined him by “grounding him” at home and taken away his mobile phone.