Detectives are appealing for witnesses following a serious collision in Ruislip.
They are also urgently trying to trace the family of the female pedestrian who remains in hospital in a critical condition.
The woman, who is possibly from the local area, is described as white, aged between 60 and 70 years old, approximately 5ft 3ins tall with short brown hair.
She had a pair of glasses in her possession but was not carrying a travel card, bank cards or any form of identification.
Police were called at 19:07hrs on Saturday, March 16 to reports of a car in collision with a pedestrian on Field End Road at the junction with Boleyn Drive.
Officers, the London Ambulance Service and London’s Air Ambulance attended and the woman was taken to a central London hospital for treatment.
Detectives from the Roads and Transport Policing Command are investigating.
They are appealing for anyone with information about the woman to contact them. They would also like to speak with anyone who saw the collision.
Anyone with information is asked to call the Serious Collision Investigation Unit at Alperton on 020 8246 9820.
The driver stopped at the scene. There have been no arrests.