I have corresponded further and I won't copy the whole chain in case it's a bit excessive but the most recent email from JL&P said:
'I would like to clarify that at John Lewis & Partners, the changing rooms are not mixed. We have simply allowed our customers to use whichever fitting room makes them feel the most comfortable. This is not with the intention of creating an air of alarm or insecurity.
As previously stated, we believe that everyone has the right to be and feel safe, secure and respected while working or shopping. There is no place for abusive behaviour, including any form of discrimination, in our shops or in our Partnership.
Please be advised, there is still privacy and safety within our changing rooms. Each customer has their own cubicle, as they always have done, which is concealed and private.
The notion of offering an alternative space encourages segregation within our customers. Here at John Lewis & Partners, we believe in inclusivity and comfort, not to the detriment of any group of persons.
Regarding this matter, I have forwarded your case to the Director Relations department who will be in touch in due course.'
Is it reasonable to accept the point that the cubicles remain private? I mean, I used to feel comfortable that I could step out of the cubicle to show a friend my clothes or to look in the mirror outside the cubicle, but I guess that's not necessarily something we are obliged to be able to do?
It does feel a bit disingenuous to say that the changing rooms are not mixed sex. If you are inviting a man who identifies as a woman to use the changing room they feel most comfortable in, and they choose the female changing room, then surely it is...?
NB the person at JL&P has not been able to explain to me how the policy isn't discriminatory towards women who have strong religious beliefs that preclude them from sharing a mixed sex space for changing. (I guess that's because they don't consider them 'mixed sex')