The system has been in place for at least 50 years. In my mum's day it was a common past time for her and her brothers to go hunting for what they called "glass

The system has been in place for at least 50 years. In my mum's day it was a common past time for her and her brothers to go hunting for what they called "glass cheques". The idea is to avoid it ending up where it shouldn't by incentivising good behaviour. If people can return the glass for money then few of them end up on the beach.