Like @MyAmpleSheep I've been struggling to interpret WR1992 in light of EA2010: a lot of the discussion has been about 'ought' rather than 'is' and doesn't take into account that the legislation overall may contain defects or inconsistencies (due to bad drafting, or as an artefact of the litigation that's already happened).
It's obvious from Hansard and the explanatory notes that the legislature genuinely intended that men with GRCs should be treated as women for Schedule 3 purposes, except in the most limited of exceptional circumstances. The whole thrust of this legislation is abusive to women.
The SC decided to reverse this on the grounds that the PMOAALA underpinning Schedule 3 must be sex-based not legal sex-based, because what possible difference could a piece of paper make? (TRAs could legitimately point out that the true significance of the GRC is to prove that some gatekeeping has taken place, but, no matter, we have the decision and are bound by it.)
The way EA2010 is structured means that the single-sex exceptions provided by it are vitiated if single-sex status is not rigorously maintained (let one in, you must let all in). This does not apply to WR1992 because the operation of WR1992 does not require, and is not provided with, a SSE under EA2010.
In both decisions WR1992 has been interpreted as sex-based (correctly - its underlying objectives must surely bear some relation to the PMOAALA underpinning the Schedule 3 application to service providers' single-sex toilets and changing rooms) but with employer discretion to exceptionally allow in certain men.
Sutherland says this was not harassment of Kelly on protected belief grounds because she has adequate other provision.
Kemp finds the opposite. (But fails to find harassment on sex grounds or indirect sex-discrimination.)
Conclusion: to meet Sutherland's 'moral propriety' requirement, people with the PC of GC-belief must be provided with sufficient single-sex provision.