Two men were arrested following the robbery of a cash-in-transit van in South Norwood.
Flying Squad officers saw the robbery at the Shell petrol garage in Portland Road at about 2.30pm on Monday, February 27.
The two suspects then drove away before crashing into another vehicle in Grange Road.
A police officer fired a gun during the course of the arrests, a spokesman for the Metropolitan Police said.
The driver of one of the cars, a 70-year-old man, was injured in the collision and taken to a south London hospital.
His injuries are not deemed to be life-threatening.
A 27-year-old man was arrested at the scene on suspicion of robbery, and a 26-year-old man was found by officers in a home nearby.
Police used a Taser while arresting the second suspect.
Both men have been taken into custody at a south London police station, where they remain.
A spokesman for the Met Police said: "The Met's Directorate of Professional Standards has been informed as a matter of course.
"Enquiries continue."
Did you see what happened? Email sean.morrison@london.newsquest.co.uk or call 0208 722 6363
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