Five Wiltshire police officers on an inquiry in south London arrested two armed men when gunfire broke out at a bus stop.
The officers acted when they saw a gun being drawn as the men started fighting in Knights Hill, west Norwood, at 1115 BST on Thursday.
One of the suspects was hit twice in the leg.
Two automatic handguns were found and both men were arrested in connection with firearms offences.
Rapid actions praised
A senior Scotland Yard officer praised the Wiltshire officers for their "bravery and quick action".
Assistant Commissioner Tarique Ghaffur, Head of the Met's Specialist Crime Directorate, said: "I have personally contacted the Chief Constable of Wiltshire Constabulary to congratulate her on the conduct of her officers and to commend their bravery.
"Their assessment of the situation and rapid action to apprehend two suspects may well have prevented members of the public being injured.
"This has resulted in the removal of two deadly handguns from the streets of London".