PC Sophie Scott was on the Victoria line platform at Stockwell waiting for a southbound train taking her to work in Brixton.
She heard the echo of people in one of the foot tunnels before a man, aged 40 and dressed in a suit, appeared to run across the platform and, unable to stop himself, fell over the edge and landed on the tracks.
PC Scott and two others tried to talk to the apparently drunk man. A member of public pressed the emergency button and tried to alert staff.
Scott then leant over from the platform to help the man off the tracks, but couldn’t reach his outstretched hand.
When the officer saw the light of an approaching train in the tunnel, she starting shouting at the man to lie still, face-down between the tracks.
She kept talking to him after the train had stopped, and shone her torch on him. After five minutes the man responded to PC Scott and stuck his head up. The tube and platform were evacuated while the man was rescued.
A spokesman for British Transport Police said: “The actions of PC Scott potentially saved this man’s life and shows the challenging environment in which police officers work.
This incident highlights the need to be careful while travelling. We advise that you only drink in moderation if you plan to use the rail network.
It is important to remember that police can issue you with a Penalty Notice for Disorder if we believe you are drunk or have committed and alcohol-related offence.”