Devon and Cornwall police, as well as the Dorset force, announced the move in July after trialling the technology since November 2015.
It has now been revealed that it could be used to respond to terror attacks, support armed operations and assist searches for suspects.
Scotland Yard began testing how an unmanned aerial vehicle could help across a range of activities.
During the eight-week trial the device, loaned to the Met by Sussex Police, will be available to officers dealing with incidents where air support may be useful.
This could include searches for high-risk missing people or suspects, serious traffic collisions, weapon sweeps and identification of cannabis factories.
The device will be on hand to give aerial support for pre-planned and spontaneous