There has been an update.
In correspondence with the complainant, the management said that there were some singles sex changing facilities. So she returned to the Leisure Centre today and got directions. You had to walk through the mixed sex area (where the naked men had been sauntering around yesterday). She found the door.
There was a notice on the door. it said that between 9am and 5pm Monday to Friday, members of the public would need to use the communal area because the single sex rooms were reserved for schoolchildren.
There was a man reading the same notice and looking for a more private changing facility. He said that he felt very uncomfortable in the shared space and needed an alternative to mixed sex provision, too.