Danny, to hazard the journey to and from the RAF Ski School, let alone the risk of injury there, is one thing. To deliberately abandon a fully serviceable aircraft in mid flight is another. Thank heavens that the exigencies of the Service saved you from such foolhardiness!
In contrast you have obviously seized the white hot heat of technology with your 2 guinea (always the mark of an upmarket purchase!) ball point pen. Miles Martin? Was that the Miles Aircraft Company? Weren't they doing something else high tech then, the M52?
As to your Camera Obscura, that rings a bell. At RAF Bicester, the pre war Station HQ had such a device set in its roof. The idea was that the release point of practice bombing aimed at a fixed "ground zero" was plotted with it after the release (from Tate and Lyle Syrup Tins) of a "cloud" of a chemical substance, though its exact sort eludes me at the moment. Thus the variation from the "DS" correct drop point, given the upper winds could be passed to the trainees and their instructors. Whether this system could be applicable to your trials and your chedlets, you would know better than I. Perhaps it was an attempt to assess their ballistic performance?