As the rate of stabbings and shootings across the country surges, Tonight explores a key driver behind the rise in knife and gun crime - the criminal networks supplying drugs, often involving young and vulnerable children. Allegra Stratton investigates the phenomenon known as 'county lines' where children as young as 10 are sent to rural areas and small towns to sell Class A drugs and talks to the frontline police working to break up gangs and disrupt supply lines.