British police were investigating newspaper reports on Friday that a body found on the roof of a building in southwest London was that of a stowaway who had fallen from the undercarriage of a plane as it came in to land from South Africa.
The man's body was discovered on an office roof in Richmond on Thursday morning.
Shortly before, another man had been found unconscious in the undercarriage of a British Airways jet that had just arrived at nearby Heathrow airport from Johannesburg. He was taken to hospital in critical condition.
"At this time there is no evidence to link the death to the discovery of a stowaway in the undercarriage of a plane at Heathrow Airport," police said in a statement.
"However this is one line of enquiry into identifying the deceased and the circumstances of his death."
Police said the surviving man had been found about an hour earlier.
"At around 8:30hrs on 18 June police at Heathrow Airport were called to reports of a suspected stowaway on a flight from Johannesburg to Heathrow," they said.
"The man, believed aged 24, was found in the undercarriage of the plane and was taken to hospital. His condition is now described as critical."
British Airways said in a short statement that it was working with police and authorities in Johannesburg "to establish the facts surrounding this very rare situation."
Bodies have previously been found in the street in the Richmond and Kew areas of London which lie below the point at which many jets open their landing gear doors to put the wheels down on the Heathrow approach.
Experts say the chances of a stowaway managing to avoid either being crushed by the wheels as they retract after take-off or being frozen to death during the flight are very small.