Retailers in the West Country have been accused of putting lives at risk - after being caught selling knives to underage children.
In the South West nearly one in four shops tested had broken the law, with one teenager being sold a machete.
The Local Government Association said the results were "alarming".
In a series of test purchases carried out by trading standards officers and police in Devon and Somerset, police cadets were sent to see which stores sold items to those under the legal age.
Seven out of 29 shops tested sold under-18s knives.
Two of these were major supermarket chains.
The blades ranged from machetes and lock knives to kitchen knives.
CHILDREN AND KNIVES: THE FACTS
shops tested sold blades to the under-18s
annual rise in knife crime in England and Wales
of people found carrying knives or involved in knife crime who were under 17 in Avon and Somerset
At one shop in Bristol, a 14-year-old girl was sold a 9 inch serrated knife.
Afterwards she said: “It’s scary how easy it is to buy a knife.”:
Retailers currently face six months in jail or fines of up to £5,000 for underage knife sales.
It’s against the law to sell knives to anyone under the age of 18 and ID should always be sought if the seller is unsure, in the same way they should be checking ID for young people buying alcohol.
Councils are calling for tougher sentences for illegal knife sales
Simon Blackburn, chairman of the LGA's Safer and Stronger Communities Board, said: "Despite most retailers passing test purchases of knives, trading standards teams at councils across the country are uncovering some shocking abuses of the law.
Knives are lethal weapons in the wrong hands and it's vital that shops do all they can to prevent them falling into the hands of young people. Just one illegal knife sale could have tragic consequences
Police say the shops that failed were notified that a test purchase had taken place and the managers and staff members who sold the knives were spoken to by officers and questioned under caution.
Prosecutions will now take place, but the form this will take will be decided on a case by case basis.