I have to say I doubt what Melanie Field is saying. I think it unlikely that the policy instructions specially addressed the issue of whether males with a GRC were to be considered female for the purposes of the EA. And I say that as an official who has been a lead on a Bill team.
The lawyers would have pointed out the difficulties with that as the Supreme Court sets out as would parly counsel. Plus as the Bill lead when you get the drafting back, you scrutinise it and if you think it doesn’t give effect to the extent of your instructions then you send it back with that query.
perhaps an FOI for those policy instructions might be illuminating? But I also think she’s overstepped. As a civil servant you don’t make public statements as your role is to implement the will of Ministers - not give commentary on your own views which frankly are and should remain irrelevant.