One in four traders are selling knives to underage shoppers, a new study shows.

Essex Police put retailers to the test by sending under 18s in to try to buy the weapons. The association has described the results as “worrying” - and said it could be a cause of the 20 per cent rise in knife crime across England and Wales.

Of 725 test purchases by London Trading Standards and police across the capital in 2016 - eight knives and blades were sold were children as young as 13 every month. A total of 96 were successfully purchased.

According to Essex Police in 2016, the situation was better here. From an operation using a selection of 16-year-old mystery shoppers, 20 stores which sold knives were visited. Seventeen of these refused to sell knives to the underage customers.

Three stores which failed the test have been visited by Trading Standards and the police and ordered to step up their checks and be more vigilant in the future.

In a previous investigation in October last year, the Echo told how a boy in Basildon was able to buy a three piece utility knife set from Poundworld, in East Walk.

The store was handed a warning notice by PC Chris Burch and PCSO Ian Grant, from Basildon’s community policing team, and no further breaches have been made.

At the time of the investigation, Mr Burch said: “This is why we have the challenge 25 policy, because we need to restrict the sale of knives to make sure they don’t get in the wrong hands.

“Staff at Poundworld were very disappointed that they had failed.”

Dangerous as the knives were, much worse has happened in these national investigations.

In the investigation, a teenager was sold a machete and a 14-year-old managed to buy a nine-inch serrated knife.

The Police said that greater fines and tougher sentences are needed for irresponsible retailers breaking knife sale laws.

Speaking on the issue last year, Simon Blackburn, chairman of the Local Government Association’s safer and stronger communities board, said: “Despite most retailers passing test purchases of knives, trading standards teams at councils across the country are uncovering some shocking abuses of the law.

“Knives are lethal weapons in the wrong hands and it’s vital that shops do all they can to prevent them falling into the hands of young people because just one illegal knife sale could have tragic consequences.”