MrsRobinson: I was going to suggest putting a rubish bin next to the wall but that hasn't helped I(p)W so I doubt it'll help you
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Nah, I don't really think it would, plus the council would probably come & take it away (or someone else would). Passersby can't manage to chuck stuff in the bins when we have them out overnight before the morning on which they are collected.

Unlike IPW's, the wall between our garden & the pavement is approx waist high - and to be fair, sometimes I think they have littered on the street & then the wind blows the stuff into the gardens along here (not that that's any better, but just saying maybe they weren't
actually aiming for the garden - lol).
IMO, there is a population density & location element to it all (probably plus lack of public/council bins to some extent), as well as lots of takeaways & shops in the general vicinity. We were up in the rural wilds of Northumberland last week - where there are hardly any people by comparison & town centres are few & far between, and things were much cleaner up there. Lol!