Actually I found more a couple of streets away at https://www.openstreetmap.org/note/4661001#map=15/51.51671/-0.07587&layers=N where new toilets are under construction. The hoardings even show a staircase leading down to the old underground toilets here, but the area has been repaved. Glass blocks in the pavement (providing light to what is now a hidden basement) are all that remain.