Staircase 'Ghost' Picture

This picture is one of the most famous 'ghost' pictures of all. Given the staircase setting and the slightly luminous figure, I had to give it a mention.
It was taken on 19 June 1966 on the Tulip Staircase in the Queen's House in the National Maritime Museum in Greenwich, supposedly when there was no-one in the field of view of the camera and shows a hooded figure apparently holding onto the balustrade with both hands. The overall impression is quite eerie - the figure appears to be on the outside of the staircase emerging from the shadows ready to catch unsuspecting visitors on the stairs. The long reach of the right arm, the apparent distortion of the stairs and the contrast between the over-exposed wall-light and under-exposed shadows, make for an unsettling picture.

The picture isn't quite what it seems, though. First, the staircase is a spiral one and the figure is actually standing on the staircase, while the viewer is looking upwards at the underneath of the steps.
Second, that long reach is more readily explained by there being another figure just ahead of the hooded figure. Rather than this being the right arm of the hooded figure, it is the left arm of the second figure, I think. I can just make out part of the profile of this figure, as indicated in the picture below. The hand we see further up could be the right hand of figure number two, or even the left hand of a third figure further ahead still.

So far, this is all consistent with information in the National Maritime Museum's website, which refers to two or three figures being present.

However, look at the hooded garment: the nature of the folds on the sleeve indicate to me a thin material, less pliable than cloth or wool; the hem at the end of the sleeve is quite prominent and the whole garment stands out from the dark background. All this is consistent, I think, with a shiny and semi-transparent plastic, most likely a lightweight raincoat with hood. June 1966 in Greenwich was the second wettest June during the years 1961 to 1970, according to information (since removed) on the Met Office historic station data web pages. So, what do we see here? Ghosts, or two or three visitors, one of whom came prepared for the weather, captured in a photograph taken under challenging lighting conditions?

Well, let me know what you think!