A number of shops in Preston have been caught selling knives to children.
The shopkeepers were busted after police carried out a series of test purchases alongside Lancashire Trading Standards last week.
The tests were conducted after police received reports from the public of shops selling knives illegally to children.
Police and trading standards officers hired children to visit shops around the city were illegal knives had reportedly been sold to minors.
It is against the law to sell a knife to anyone under 18, unless it is a penknife-type object with a folding blade less than three inches long (7.62 cm).
Lancashire Police said test purchases are conducted every month across the county to stop children purchasing items which are illegal for them to buy.
Last week, a number of shops failed the tests and were caught 'red-handed' selling kitchen knives and snap-knives to children as young as 15-years-old.
These include alcohol in pubs, clubs and off licences, knives, tobacco and gaming machines.
Police are asking for anyone with information on sales of items to children to get in touch.
The force has given its assurance that it "always follows up" on reports of this nature.
A spokesperson for Preston Police said: "Last week we were working with our colleagues in Lancashire Trading Standards on test purchases of knives.
"Where we get information from the public about shops selling illegally we run test purchases on the shops to see if they will sell to children.
"Sadly in our latest visits, a number of shops have been quite willing to sell knives to the test purchasers.
"Basically its illegal to sell a knife to anyone under 18, unless it is a penknife type knife with a folding blade 3 inches long (7.62 cm) or less.
"We do test purchases for alcohol (both pubs/clubs and off licences), knives, tobacco and gaming machines at least every month.
"If you have any information about sales of these items to children, let us know.
"We *always* follow up."
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If you have information which can help police please call 101 or report it via the Lancashire Constabulary website.
Alternatively you can call Crimestoppers anonymously on 0800 555111.