Commander Tony Eastaugh said:
An innocent family are now dealing with the tragic loss of a loved one.
The Metropolitan Police has now begun a thorough investigation into the circumstances of this terrible incident.
The thoughts of our staff and officers are with the family at this time.
Traffic police and officers from the Directorate of Professional Standards are now investigating, the force said.
The Independent Police Complaints Commission has also been informed and an investigator was at the scene assessing the circumstances of the collision.