Police and Trading Standards officers swooped on a number of shops in a crackdown on knife crime.
Test purchases were carried out by young people who looked too young to buy a blade.
Several shops were willing to sell knives to young people.
A police spokesman said: “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.”
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The law states it is 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
Police and Trading Standards regularly carry out 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 call police on 101 number, or via the Lancashire Constabulary website or via Crime Stoppers on 0800 555111.