Crime

How to stop the phone-snatchers in London:

Get plainclothes police walking in phone-snatching hotspots wearing a backpack or ideally a garment which conceals a drone. 

When a cops witnesses a phone-snatch, the cop takes out the FPV drone and chases the thief with it.

The drone can have a speaker and be flown to follow the suspect until they are apprehended, and could even mark the suspect using the blue paint method.