With reports this week that British teachers have begun patrolling the streets in a bid to combat the so-called "knife crime epidemic", this video shows just how hard the task may be of identifying pupils carrying blades.

The clip shows a British man holding what looks like a pen which he claims he confiscated from a 12-year-old schoolboy in London.

The viewer understands why he took it when he pulls the ballpoint apart to reveal a 5.5-centimetre blade hiding in the shaft.

The man claimed the boy, a friend of his son, was showing off the knife before school and said he had bought it from a popular shopping website.

The clip was filmed back in January.

This guy on our building site told us he had taken this pen/knife from a 12 yo boy this morning, parents and everyone need to be aware and check there children’s bags for these type of things, they think ther cool and fashionable, but in actual fact there destroying lives.

Was filmed on a building site in east London(silvertown) not sure the names of the guy as it was random person on site who had the object, he was showing a friend when I came over to look at what it was and the guy was heard saying h took it off a sons friend before school, he said the boy got it online from a shopping website. It happened today at around 8:30am when I filmed it.