Police are searching for a suspected gunman who appeared to point a weapon at officers following a car crash.
Officers initially tried but failed to stop the vehicle in Harlesden High Street, in Kensal Green, north London, and again pursued it with "blue lights and sirens" after spotting it in nearby Victoria Road.
The man, being originally chased in connection with a burglary, jumped from the car apparently brandishing a weapon after it later collided with another vehicle on the A40 in North Acton.
"Firearms officers were called to the scene along with the National Police Air Service and an area search was conducted," said a police spokesman.
No arrests have been made and no one, including the man in his 50s in the other car, was reported injured.
Detectives from the Trident and Area Crime Command are investigating and enquiries are ongoing after the incident at 8.45am on Thursday 29 December.
The Met Police refused to say why or how they lost track of the suspect.
Police are appealing for witnesses to call Crimestoppers on 020 7230 2171.
