From the video it looks to me like a flashbang, MK5/MK7 or a firework. The shop windows stay intact, and there’s no evidence of any penetration of projectiles after the blast.

Could also be a crow scare packaged in a fake grenade shell, like the kind of thing paintballers/airsofters would use.

inb4 the supreme court rules that congestion charging is unconstitutional and furthermore that public transport, too, is unconstitutional.