I am curious about the Ministers staircase , it seems natural that there be a staircase there ..to me at least. but what was that space originally for??? and does anyone have a floor plan of the original Buckingham house and the original palace before it was built on to ?
I've never personally seen a floorplan of Buckingham House, but since the enlargement of the main block by Nash basically retained the original footprint, we have some clues from the present floorplan so generously posted by Architect. The "core" house (excluding the two original service wings) consisted of the present Guard Room and Staircase (space), the Green Drawing Room (formerly Queen Charlotte's 2 story Salon), the Throne Room (or at least the southern most part of it), and the Picture Gallery behind (which was originally separate garden facade rooms). Nash, of course, combined the original garden rooms into the Portrait Gallery and added a new suite of rooms behind it (White Room, Music Room, Blue Room).
Imaging the current floorplan without the added garden suite, the location of the present Minister's Staircase seems illogical to me. It would have been located stuck in the NW corner of a garden front room. More likely that "space" was part of the ancillary / service rooms forming the two original wings, which Nash demolished.