In such cases, British anti-discrimination law mandates a kind of thought experiment, considering whether the treatment would have been different if everything apart from the protected characteristic had been the same. Green argued that the comparison should be with a (non-trans) woman; the prison governor, that it should be with a (non-trans) man. This gets to the heart of the matter. If gender identity defines whether a person is a man/male or woman/female, when you take away a transwoman’s ‘transness’ you get a (cis) woman. But if biological sex does, what you get is a (cis) man.
