I'm surprised that many people say that they've never seen a nitrous oxide canister. When I was teaching, our school grounds were always littered with them on a Monday morning, from all the teenagers who'd entered the site over the weekend and used them - and that was over 30 years ago! I actually seem to see far
fewer of them these days than I used to!
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Litter has never been a big problem, in the 30 years since I've lived here, in this small Suffolk town (pop. approx 5000). Most people don't drop litter and we've got an excellent litter picker, employed by the town council, who picks up what little does get dropped. Someone walking the full length of the main street (about a mile) might struggle to find a single dog end on the ground, with the housing areas being just the same. (My house and garden are as unkempt as it's possible to be but, if I see a piece of litter out in the street, I'll always pick it up and put it into my bin. Most other householders around here are equally vigilant).
In many ways I miss the big city where I used to live (Sheffield) but I certainly don't miss its litter. In those days, anyone walking anywhere near to the markets area on a Saturday afternoon would, quite literally, find themselves ankle deep in litter.