Teenagers taking part in an undercover investigation were sold a variety of knives without being asked for ID in shops across Warwickshire.
Trading Standards Officers visited 54 shops in Atherstone, Rugby, Nuneaton and Bedworth, Warwick, Leamington and Stratford as part of the undercover operation.
They found that one in five Warwickshire retailers failed to ask for proof of age when selling knives to young people.
In one in every five shops investigated, Trading Standards teenage apprentices were able to buy steak knives, kitchen knives and Stanley knives without being challenged about their age.
Warwickshire County Councillor Andy Crump, portfolio holder for Community Safety said: “Retailers have a part to play in tackling knife crime by helping to prevent knives falling in to the hands of young people.
"I’m delighted that the majority of our retailers are taking their responsibilities seriously and asking for age identification.”
“However, a 20 per cent failure rate is too high and this is why our Trading Standards Service has been providing advice and guidance to retailers.”
Best practice is for businesses to routinely ask for age identification before selling any age restricted product to anyone who appears to be under the age of 25 (Challenge 25).
All retailers were provided with advice on preventing the sale of knives to children.
And officers then returned to the premises that had sold knives, with volunteers aged under 18.
The under aged volunteers were able to buy knives at three of the premises - a criminal offence. These shops were located in Nuneaton, Bedworth and Warwick.
Retailers are being advised to introduce Challenge 25 and train their staff to ask for proof of age, keep knives locked away and put up posters to dissuade young people from trying to purchase knives.
Trading Standards Services across England and Wales have been carrying out similar test purchase exercises in which they ask child volunteers to attempt to purchase knives from retailers. 2,231 test purchases were carried out and 344 sales made.
Retailers who sell knives to children could face prosecution - potentially facing up to six months in prison and a £5,000 fine.
More information on the work of Trading Standards can be found by clicking here.