Created by the Pritzker prize-winning architect Shigeru Ban and more than a dozen other leading designers, the toilets are made from coloured ‘smart glass’ that turns opaque when the cubicles are occupied.

Non-profit organisation Nippon Foundation, which organised the Tokyo Toilet Project, said there were important practical and hygiene considerations behind the unusual toilets.

“There are two concerns with public toilets, especially those located in parks,” it told The Guardian. “The first is whether it is clean inside, and the second is that no one is secretly waiting inside.”