PC Morgan Younger tackled the suspect, who was allegedly trying to stab another man, at a petrol station on Lee High Road on Saturday, January 25.
He managed to restrain and disarm the man while calling for help.
PC Younger, who has five years of service, was on patrol when he stopped at the petrol station to buy a drink.
At the entrance, police say he saw a man grab the victim around the throat and attempt to stab him with a large knife.
The officer responded, grappling with the suspect while he continued to wield the knife.
He managed to bring him to the floor and disarm him without any help.
He then says he restrained him single-handedly while calling for back-up and still managing to arrest the man on suspicion of attempted murder and possession of an offensive weapon.
He kept the man under control for five minutes until further officers arrived to help.
The man, in his 60s, remains in custody at this stage.
He was further arrested on suspicion of handling stolen goods and being concerned in the supply of Class A drugs, after a quantity of drugs was found at his home address.
The victim, aged in his 40s, was not injured.
Deputy Assistant Commissioner Jon Savell said: “This is outstanding work from an officer who was on patrol alone, saw a very violent crime in progress and, without hesitation, raced in to assist.
“I cannot overstate how proud we are in the Met today of his quick-thinking and bravery.
“He was calm and professional and everything we want our police officers to be.
“I have no doubt without his intervention, the victim would have been seriously injured.”
