Police are searching for a man called Steven Palmer after a serious car crash in Uxbridge on Sunday.
Officers want to interview Mr Palmer, 27, about the crash on Harvil Road, which left a woman in a serious condition in hospital.
Louise Clark, 38, had to be cut out of her car, while the other driver fled the scene on foot.
Officers are asking anyone who may know Mr Palmer's whereabouts to contact police, and appeal direct to Mr Palmer to come forward.
Police also want to talk to a driver who may have witnessed the incident driving a light or white coloured Fiat 500.