Breastfeeding's already covered in legislation, and Sally Mann's a pretty complex example, not really relevant to a discussion about photography in public.
I'm definitely not an expert! but I'm not seeing the level of nuance in these last few posts that's being suggested. I didn't want to spend ages googling case law, but most of the convictions for indecent photography in public that I could find were pretty extreme cases. Those are probably the best guide to what judges and juries actually count as indecent.
If convictions are rare and reserved for extreme cases, the fear of false accusation is probably overstated too.
I've kept my own ethics out of this, because they're not really relevant to a discussion about how the Home Office guidance contradicts UK law, and what that does to photographers. There are definitely photos I wouldn't take, not because they're indecent, but because they don't sit right with my own values. Bringing ethics into it just muddies the waters, and it adds to the confusion this thread was trying to clear up in the first place. We all set the bar different, but that doesn't make it law.
This thread started out about the Home Office advice contradicting UK law on photography in public, and how that confuses photographers and the public about what's actually legal. Now we're adding to that by suggesting girls in costumes, or photos of consenting adults at a public protest, could be indecent. That's just adding fuel to the fire. Next it'll be someone doing flower photography in the park getting challenged by a worried parent because there are kids nearby. We need some common sense and pragmatism here.
As we keep getting drawn into the ethics of public photography, I'll probably leave the thread for now until the conversation moves on, otherwise we're going round in circles.