Five stores in Preston were caught selling a knife to a 15-year-old during a sting operation by police.
During Monday 13 May eight city stores were visited by the teenager who attempted to buy a knife.
Three stores challenged the 15-year-old but five stores were given a warning by police and Trading Standards after failing the test purchase.
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Police Sergeant Ste Tillotson said: “Knives are dangerous and the sale of them to children is not only illegal but puts them at risk too.
“All of the stores we visited were reminded of their responsibility when it comes to refusing sales to under-18s.
“If you have any information on young people purchasing knives in local shops, please do contact us so that we can take appropriate action.”
County councillor Michael Green, cabinet member for health and wellbeing at Lancashire County Council, said: “I was out with our Trading Standards Team in Preston yesterday and was appalled to see the majority of the businesses selling knives to a 15-year old.
“Knives have no place on Lancashire’s streets and Lancashire County Council is committed to working hard with the Police to tackle this issue and keep our young people safe.”
Anyone with information about knife crime can call police on 101 or report anonymously through independent charity Crimestoppers on 0800555111.
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