But it's my understanding that if you are sued, having ignored the advice from the EHRC, courts would take a very dim view.
EHRC produce two sorts of advice - statutory code and non-statutory guidance. The statutory code holds a lot of weight in court, the non-statutory guidance not so much.
Unfortunately, this is non-statutory guidance and the statutory code still contains 'case-by-case' and other things that are very difficult to work with.
EHRC really now need to update the stat code. They were asked to do so following the EA inquiry:
Recommendation 15
We do not believe that non-statutory guidance will be sufficient to bring the clarity needed in what is clearly a contentious area. We recommend that, in the absence of case law the EHRC develop, and the Secretary of State lay before Parliament, a dedicated Code of Practice, with case studies drawn from organisations providing services to survivors of domestic and sexual abuse. This Code must set out clearly, with worked examples and guidance, (a) how the Act allows separate services for men and women, or provision of services to only men or only women in certain circumstances, and b) how and under what circumstances it allows those providing such services to choose how and if to provide them to a person who has the protected characteristic of gender reassignment. (Paragraph 190)
publications.parliament.uk/pa/cm201919/cmselect/cmwomeq/96/9602.htm
It's interesting that they've more or less done all this now, except for making it statutory.