A quick-thinking bystander who brought a police chase crashing to a halt is being urged to come forward so officers can thank him.
Footage released by police in Kingston upon Thames, south-west London, shows the man, praised as a "legend" by the force, casually tripping up a suspected drug dealer as he is pursued on foot.
With his hands in his pockets the man is seen to stretch out his right leg, bringing the suspect to the floor, before striding away arm-in-arm with his female companion.
The video was widely shared and viewed more than a quarter of a million times on social media after it emerged online on Thursday evening.
Pc Sebastian Ellis from Kingston Borough said: "We are very thankful to this man for his swift intervention that helped the officers detain the suspect.
"The video was brought to the attention of the Borough Commander who was very impressed and would like to meet the passer-by.
"So if you are reading this article please get in contact with me."
Police on patrol were made aware of a report of two males seen dealing drugs on Clarence Street, Kingston, late in the evening on Saturday February 6.
A Scotland Yard spokesman said: "The males left prior to the arrival of police but one of them was stopped by police near to the scene.
"Officers attempted to speak to the male who then made off.
"With the help of a member of the public he was detained a short time later.
"The 17-year-old youth was arrested on suspicion of possession with intent to supply Class A drugs."
The boy was taken to a west London police station, and bailed until early April, police said.