At the last minute. It seems that the women of FiLiA would endanger other conference delegates, as the reason given is "the need for our delegates from all backgrounds to feel as though the party conference is a safe space for them to express their identity comfortably". It seems the party lives in a topsy-turvy world where women are a threat to the safety of men. It clearly hasn't made much progress in detoxifying its culture of misogyny.
Is Wales not covered by the Forstater judgment? The Equality Act certainly applies there.