Trading Standards officers in County Durham are promising tougher action against shops selling alcohol to underage children.
The pledge follows operations in several towns which saw traders selling alcohol and cigarettes illegally.
Durham County Council said it was targeting shops in Crook, Stanley, Barnard Castle, Ferryhill and Consett.
In recent test purchases more than 10% of traders flouted the law and sold alcohol or cigarettes to youngsters.
'Follow up visits'
A council spokeswoman said: "Our commitment to step up action against underage sales has made an early impact and raised awareness among businesses in the county that they must improve their procedures to prevent illegal sales.
"It's clear that staff still do not appreciate how difficult it is to judge the age of teenagers and so should always ask for identification.
"Follow up visits will be made to all those who made illegal sales and if there are more, prosecution will be the likely outcome.
"We are determined to reduce the incidence of alcohol fuelled anti-social behaviour."