Unisex etiquette

Unisex toilets are pretty commonplace now, being mostly just simply rows of cubicles (which each contain a toilet & sink) in the one space.

However, what about one that is just a small room containing just the one cubicle within it?
The unisex toilet in the reception area at South Staffordshire Council Offices in Codsall is a little tricky. In this instance, in the one small room (with hand-basin) and the toilet cubicle.

So, does one queue inside the room, ie standing by the hand-basin - or outside the room's main door?

I wasn't sure how the woman who went in before me would feel about standing by the basin, next to her cubicle, waiting for her to finish. 
I decided to wait outside the door.