I swim regularly at Ponds Fords and use the competition pool changing rooms.
They do get used as an access to the competition pool by lifeguards, coaches and other staff, and girls going to the diving pool. Staff also use the toilets, and as they are at the far end nearest the pool, they have to walk through the main part of the changing rooms. There are toilets in the gym changing room and the leisure pool changing rooms but I dont know if staff use them too. The only non-changing room toilets I know of are on the next floor up.
There are about 5 cubicles in the changing room, but during a competition I imagine there could be around 50 or more women/girls in there, so its not like everyone who wants a cubicle is going to get one.
Whenever I have been there it has only ever been women and girls passing through, but even so, I do feel more self concious if there are groups of what can be very young girls (age 6+) going by.
As a PP has said, the pool can be accessed directly from a public corridor, which is a shorter route than going through the changing rooms. I don't know why this route isn't used.