Apologies if this has been discussed before. Two years ago the government responded to a petition calling for self declaration, quite clearly against such a move.
petition.parliament.uk/archived/petitions/104639
It doesn't particularly go into womens spaces or womens safety, but the jist can be summed up as A person’s gender has important legal and social consequences. The state has a legitimate interest in ensuring that people who take on a new legal status can establish that they meet certain criteria.
Has their position suddenly changed?