Misrepresenting the law does leave Stonewall Diversity Champions vulnerable to legal actions and even class actions from their female/gay/lesbian/bisexual staff at any time in-the-future.
Legal Feminist has highlighted the risk that organisations associated with Stonewall, and in particular its corrupted interpretation of human rights law attract.
It's unlikely most HR Directors have read that advice, but if a Company or organisation maintains a proper Risk Register, having an entry related to being a Stonewall Diversity Champion should be an expectation. Of course that risk can be accepted, or perhaps more sensibly, mitigated, by leaving the scheme.
Legal risks for Stonewall members
As a HR Director, knowledge that your career (and pension) might be at peril if you persist in maintaining a relationship with Stonewall, at the possible cost of seeing your employer subjected to a High Court action by its employees/ex-employees, is surely diffusing through the profession.