Newcastle Upon Tyne: We built this city on sausage rolls

So apparently, I found someone else's rubbish in my recycle bin. Mind you, the shed it's stored in only has ~5 recycle bins, mine is numbered with my flat number, and they were dumb enough to leave a parcel box with their own address on it, which shouldn't even go into any of these ~5 bins.

While it shoudln't be a huge problem, if their shit contains anything that makes the bin men refuse to take the rubbish, I would be alone with the problem, and they also left half a pack of canned beer, and some of them are still oozing beer. Together with my own, the bin is kind of full,

On the other hand, it feels really petty to complain about some rubbish in my bin. Also, I may look/feel like a weirdo/pervert if they ask how I found them, because that indicates that I went through all of their rubbish to find that parcel box with the address on it. Even though I think they did this to themselves by dumping their waste into someone else's bin.

What would you do? On a scale from "don't even bother" to "Report them immediately", how serious is this matter? Is it worth doing anything about it?