There are two theories for this piece. One theory is that it is an unidentified piece by Topshop, because Topshop sold a dress that was in a different cut but used the same print. The other theory is that it is a romper made by Basic Editions in the 90's. Only one has surfaced that I know of, and that was in a vintage shop on Etsy. I tend to think that it is the romper, because in the brief flash of her legs you get it does look more like a romper, and she is wearing that same black undershirt she wore with her other rompers. As far as we can see it, the cut and print appear to line up identically to the romper. As for Topshop using the same print, I think that's just a coincidence, as it isn't uncommon for designers to recycle vintage prints. Here is the link to that Etsy listing if you want to look at more reference pics yourself: https://www.etsy.com/transaction/179772966 I don't have a link to the topshop dress.
Worn in: Journey to the Center of the TARDIS (outfit #2)
Urban Outfitters Sparkle & Fade Blue Loose Fit Playsuit
I know nothing about this piece except its name. (I don't like rompers personally, pick either a dress or shorts and stick with it.)