Deteriorated edition. This was taken with a Six-20 Brownie 'C' which produces pleasingly large negatives which are vast compared to the assumptions that the scanner makes (eg 35mm at some vague location in the middle of the glass).
So... pending the arrival of a properly dark darkroom I took the backlight to pieces, extracted the translucent plates and held a light while a normal scan was taken. A stationary lamp might have been more effective but a result was produced nonetheless.
Thanks are due for HP5+ rewound onto 620 reels kindly provided by Alastair Cook.