A man died at Streatham station on Saturday morning after falling off the platform on to the tracks.
It is believed the 23-year-old stumbled off the platform and was electrocuted after coming into contact with the live third rail.
The incident was reported at 6.23am and is being investigated by the British Transport Police (BTP).
A BTP spokesman said they are currently treating the incident as non-suspicious, adding: "Upon attending the scene officers discovered the body of a 23-year-old man from Morden.
"Paramedics from the London Ambulance Service also attended but the man was pronounced dead at the scene."
A postmortem examination has yet to take place.
Police said the man has not yet been named, but next of kin have been informed.
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