In the UK, I'd be taxed on it, and sorting that out properly would mean having to go through self-assessment. But that's not actually hard, and while I've not

In the UK, I'd be taxed on it, and sorting that out properly would mean having to go through self-assessment. But that's not actually hard, and while I've not needed to fill in that particular bit, the extra effort it would require doesn't appear to be particularly onerous. I suspect that if you started getting any reasonable quantity of donations that would also pique the taxman's interest.