OK, so I went to my vet yesterday and took one of the beetles. My vet agreed that it didn't really look like a weevil, and probably isn't one based on how they've been living. He admitted that he has no idea what it is, but doesn't think I should worry too much because it hasn't harmed any of my hamsters.
I decided to do a little research on weevils found in the UK just to be sure, and found a picture on Rentokil's website that looked just like the beetles I've been seeing, called the Rust Red Flour Beetle.
https://www.rentokil.co.uk/stored-pr...sects/species/
I have no idea if they are actually are that species, but apparently they only eat grains that have already been ruined by weevils, which might be why they've shown no interest in my hamsters' food. The only other thing they eat is dried fruit, which makes me think even more that they are indeed Rust Red Flour Beetles.
There are apparently some species related to Rust Red Flour Beetles that
are harmful and destructive, but because these ones haven't done anything, I don't think they're that kind. As for how to get rid of them, I haven't been able to find anything.
But I'm not too worried, because they're not swarming the cages. Just in case it
does become an infestation, I'm going to give Rentokil a call to see what ways I can get rid of them. Thanks to everyone's replies, you've been a big help!