Haven't yet read past this, as it made me smile and want to post again before reading on.
So the solution is, apparently... a female-only space! With an additional space for women who don't mind mixed-sex, be they transwomen, or Piggles and other "allies".
This is the same thing we're suggesting!!!
The only difference is in the framing or perspective. But boy, what a difference that does, indeed, reveal.
Most posters appear to believe our current 100-year-old, 99% reliable, system of separate female spaces upheld by social contract is worth preserving - with an additional third space added for the minority group of transwomen and the small proportion of women* happy to share with them.
Piggles, I think, is suggesting that our current 100-year-old, 99% reliable, system of separate female spaces upheld by social contract should be reframed as mixed-sex to accommodate the minority group of transwomen - with an additional third space added for the majority of the UK's female population*.
(*My understanding is that surveys - those that are unusually clear about their definitions, at least - have shown this to be the case; apologies I don't have links, I'm sure someone else will).