A video shows the moment off-duty police officers tackled a knifeman.
On July 31 last year a fight broke out between two groups of men in Elephant and Castle.
During that fight one man, was struck over the head and fell to the floor.
Joseph Jimenez, 20, from Dalston, then stood over him and tried to slash him with a large knife.
A group of Metropolitan Police officers from the Gangs & Pro-Active Team in the Central South Command Unit were out socialising after work together at a bar and the officers rushed to the incident and separated the attacker from the victim.
Seeing the officers, Jimenez threw the knife at them and attempted to run away.
Officers administered first aid to the victim and he was taken to hospital for treatment for a head injury.
On Wednesday (February 14) Jimenez, of Baxter Road, appeared at Croydon Crown Court having pleaded guilty to affray and possession of a bladed article.
He was sentenced to eight month at a young offenders' institute.
Detective Inspector Jon Summers said: "The team had finished a long, hard week at work and were enjoying some well-earned down time together when the events unfolded.
"They had been off-duty and were without any form of protective equipment such as batons or PAVA spray, or a police radio.
"Still they intervened, working tactically together in coordinating their approach to close off the suspect's possible escape route, and swiftly arrested him.
"The heroism shown by these officers is nothing short of exceptional.
"They placed themselves at real risk of serious injury in order to prevent serious harm and to apprehend an offender. It is actions such as these that demonstrate the true heart and soul of the Met.
"They are a credit to themselves, the unit and MPS as a whole."
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