Officers were called at approximately 6.10am on Saturday, 4 September to reports of a road traffic collision on the westbound carriageway of the A40 in Ruislip. A car was found to have left the road.
London Ambulance Service also attended and despite the best efforts of the emergency services, a male (no further details), believed to be the driver of the car, was pronounced dead at the scene.
Next of kin are yet to be informed.
Road closures remain in place.
Enquiries into the circumstances are ongoing; there has been no arrests.
Anyone who was in the area at the time and who witnessed the incident is urged to call 101, or tweet @MetCC and quote ref: CAD1555/04Sep21. Officers are particularly keen to hear from anyone who has dashcam or other video footage which may have captured the incident.