Apparently it's West Yorkshire that would be the force to investigate Mermaids? That's how the article opens. I guess that may be right if that's where Mermaids is based.
Article also reveals an apparent conflict of interest which I don't think is news to this board but is likely of interest to the wider public who won't have spotted all these kinds of links and affiliations:
"In 2019, Mermaids confirmed it had provided training sessions to both Merseyside and West Yorkshire Police and that representatives from other forces have been present at one session.
In images of one of the sessions shared on social media, the slides included a scale from one to 10 with a Barbie on one side and a GI Joe on the other, and asked: “Where on the spectrum might your gender identity be?”
Mermaids later claimed that the Barbie to GI Joe scale was tongue-in-cheek.
West Yorkshire Police has refused a number of Freedom of Information requests asking for details of its contact with Mermaids, largely on grounds of cost."