Don't want to interrupt Stephen's thread as this is about trans men and I am a trans women, but I wanted to answer the questions asked from my perspective too, since they were fair and direct ones.
These are just my personal opinion, of course:
Should women's DV refuges remain single sex? Yes or no?
Absolutely. That is what the GRA allows for, and in other situations of medical procedures such as smear tests. Facilities are allowed to make individual exceptions at their discretion, but it is not a right. Nor should it be an expectation by a trans person even with a GRC.
That is how it should remain.
Should Girl Guides have unsupervised mixed sex overnight accommodation for teens? Yes or no?
I think any trans child should be accommodated in teacher facilities or single accommodation for their comfort and peace of mind of others. When I was on a school trip in the 60s it's what happened to me. As frankly no boy wanted to be anywhere near me and set fire to beds and tried to blame me having done it to ensure it happened. It hurt at the time, but I felt safer away from them and happier than I would have done being where it made others angry.
When I was teacher training we had (non trans) trips where we did the same with pupils who had needs. It usually worked best all round.
Was the Swim England trans guidance sexist when it said breasts should be covered but penises should swing free? Yes or no?
Of course it was. Either neither are deemed offensive or both are. You cannot differentiate without it being sexist.
Caucho - just to answer your suggestion that trans women outnumber trans men 20 to 1.
In the activist movement, maybe. Not sure never having met any activists.
But in numbers, it is worth bearing in mind that two of the very first four cases of trans surgery cases dealt with 80 years or so ago were trans men. So a much more even split than you might imagine.
In the 70s when I had surgery and this was the only real type of assistance then on offer the split was around 90% + trans women. And then relatively little physical options were available to trans men compared with now.
So I suspect in the next few decades on the relatively rare occasions trans people had a public profile they were mostly trans women for that reason. Though the vast majority of trans people of both genders (whichever way you look at it!) kept their heads down, were relieved to have resolved their gender dysphoria and, having no real legal rights, lived quietly without much fuss. So the isolated cases in public were those who were to some degree seeking that. Or thrust into it by nature of the media.
However, even before the last few years when more young girls have been presenting to Gender Identity Clinics saying they were boys than the other way around (and this rise was noticed and is I am sure being investigated as it was not expected I imagine) then there always was a trans men/ transwomen split much closer than the 10/90 % of the 70s.
In 2005, first full year of the GRA when many older trans people swelled numbers to claim a GRC, the split between trans men/women was not 10/90 but (in actual numbers) 269 / 912 - which as you can see is around 28/ 72%
So over a quarter were trans men.
In 2015, ten years later, it was (in actual numbers) 109 / 223 - so almost exactly 50/50%.
As you can see GRC numbers are small all told each year - in the past five years the annual totals awarded are just 236, 318, 244, 332 and 318.
That is for the whole UK in a whole year.