Look, I'm all for people researching other countries on Wikipedia, great on you!
I would just say that in very tense situations where the exact details of a law very much matters, the difference between different legal systems might be worth some consideration.
For example you link a useful police.uk document which lists a law whose wikipedia page mentions a different law applying in Scotland, where these people are.
It also links to a legislation.gov.uk page which has a "show geographical extent" feature on the left navbar. Applying this filter to the linked "Section 66" page, it shows "E+W" (England and Wales).
I'm aware that there is also some guidance about whether nipples are genitals, which might be relevant to the Scottish situation. And that nudists were specifically considered when writing some laws (as you mentioned, to protect them)
Just feel like trans people protesting in such a visible way, in a particular part of the UK, who will defininitely be featured in newspapers... it seems like they would have legal guidance from someone with a lot more local knowledge than, for example, knowing which countries comprise the UK?
+1, hope they do well, and 🙄 at the idea of british laws being consistent!