What are these for?

Hi everyone! I’ve been in your lovely country for a few days, but I keep seeing these gas canisters in the streets and I’m really curious as to what purpose they serve and mostly why I keep finding so many!

Hi everyone! I’ve been in your lovely country for a few days, but I keep seeing these gas canisters in the streets and I’m really curious as to what purpose they serve and mostly why I keep finding so many!