This is totally off topic, but does the guardian use kg because they’re relatively international or do non-human things generally use kg in the UK? I know it’s a mix with the more familiar things (a person’s height or the length of a road vs the height of a new building, for example) being imperial. I just would have expected an animal’s height/weight to be measured the same way a human’s is.
I’ve never heard a British person talk about their own weight in kg (or their own mass), it’s always pounds or stone and pounds. That could just be because I’m American and they’re really thoughtful about my units, but multiplying/dividing precisely by 14 in my head to figure out stone always takes me a moment, so I don’t think it’s that, lol.
It could also just be that I’m old enough that my peers had already finished primary school by the time the switchover was “complete.” Is it an age marker like cursive is in the US or the spelling reform is in Germany?