A queue barger at a fast food outlet crowded with schoolchildren provoked an argument which turned to bloodshed.
Detectives from Lambeth CID are appealing for information after a man with his young son and niece was injured in the Chicken Cottage, Streatham Hill, at 4pm on February 7.
The suspect entered the shop and tried to cut into the queue. When the 49-year-old victim challenged him, the suspect became argumentative. The victim tried to calm the situation and said the man could go in front of him. The suspect continued to be aggressive and then took out a knife.
The victim managed to push the man out of the shop, but he lunged at the victim who sustained a cut to his hand.
The suspect is described as a black male, around 5ft 7in tall, of slim build and with a dark-coloured patchy beard.
He was wearing a black jacket with the hood up, black trousers, and dark-coloured trainers and a rucksack. He is said to have had a South London accent.
Detective Constable Dominic Landragin said: “The suspect, when challenged about his behaviour, pulled out a knife and showed a clear willingness to use violence. This incident happened at a busy time of day in front of schoolchildren who were terrified by what they saw. I want to trace this man and would ask anyone who thinks they might know who he is to contact police.”
No arrests have been made. Anyone who witnessed the incident or thinks they know the identity of the suspect is urged to contact Lambeth CID on 101 or Crimestoppers on 0800 555 111 if you wish to remain anonymous.