Instagram is being used to promote illegal knives designed to be attractive to young women, The Telegraph can disclose.

The knives – some disguised as lipsticks or combs and highly decorous – are being promoted through the photo-sharing website. The site, which is owned by the social media giant Facebook, is accused of "reprehensible" behaviour by promoting products banned in the UK.

An investigation by the Telegraph has uncovered a trail involving a US business specialising in selling knives to women that are then imported to the UK.

This newspaper discovered a young British mother who was bought an illegal "flickknife" decorated with a mermaid, for a Christmas present by her husband. The woman even gave the knife a name – calling it "Baby". The importation of such knives is illegal under the UK’s strict knife crime laws. Instagram is used to promote the knives and link to the company’s website, based in North Carolina.

The Ben Kinsella Trust, a campaigning charity set up in memory of Ben Kinsella, a 16-year-old stabbed to death in Islington a decade ago, said it was appalling that Instagram was helping promote the US company Alien Outfitters.

"Instagram’s action in hosting this site is reprehensible,” said Patrick Green, the charity’s chief executive. “They are glamorising these knives as fashion accessories. This is a forum where young people openly encourage each other to break the law by buying flick knives and concealed knives which are illegal for any age group."