Flying Lawyer. Thanks for your posts. Very enlightening.
Given this is a military thread, I think any discussion has to appreciate the different roles the AAIB plays when investigating civil and military accidents. They are very restricted in the latter, where much of the engineering investigation is the responsibility of the SI's engineering member. Few even scrape the surface so, almost by definition, SIs are tainted and mostly incomplete.
The most obvious case, and the most debated here, is the Mull of Kintyre crash. At first, the AAIB stood by its report. When it found out how much evidence had been concealed by MoD, rendering large parts misleading and even inaccurate, it later effectively disowned it, with the senior examiner presenting himself to Lord Philip to confirm this. Lacking the concealed evidence, and a complete re-write, there is no way one could use that report in court proceedings.
I'm not convinced the court ruling allows for this!