This letter is an overt statement on behalf of M&S that the changing rooms adjacent to womenswear and lingerie departments are female-only single sex spaces. It can be treated as official clarification that customers and staff can rely on as binding on M&S
It is clear that he distinguishes between ‘women’ and ‘males’, adopting, correctly in this context (discrimination law covered by the Equality Act), the Supreme Court’s definition of ‘woman’ as being exclusively female.
The problem, of course, is that neither the in-store signage nor the day to day exercise of this policy matches what he is saying.
He must be invited to:
a) send official guidance to all stores stating categorically that changing rooms are to be treated as single-sex spaces,
b) publish that guidance openly on as many public forums as possible,
c) embark immediately upon a programme to properly sign all changing rooms and toilet facilities, and
d) impose training requirements upon all staff so that the policy position outlined in his letter is implemented effectively.