Shops in London are selling knives, alcohol and tobacco to children as young as 13.
Knives and alcohol sold to children in London
Over 2,500 test purchases carried out by London Trading Standards (LTS) revealed the age-restricted items being sold to under-18s.
A total of 285 illegal sales were recorded, with 14% of shops selling knives and 12% selling alcohol. The Met Police said it was "unacceptable".
There have been 64 fatal stabbings in London since January.
Sophie Linden, deputy mayor for policing and crime, said: "The only way we are going to rid our streets of these dangerous weapons is by working together to stop them getting into the hands of young Londoners."
Over 18 months, 26 local authorities conducted test purchases for knives, alcohol and tobacco using volunteers between the ages of 12 and 17.
Retailers currently face six months in jail or a fine of up to £5,000 for underage knife sales.
The latest Met Police figures show a 12% rise in knife crime compared to the previous 12 months, with the force recording 8,704 knife offences this year.
LTS has been working with the Met on Operation Sceptre, which aims to reduce knife crime.
Trish Burls from LTS said: "We are disappointed that a 13 year old has been allowed to buy a knife in a London shop.
"But we note the relatively high levels of compliance among the majority of retailers."