As Flying Lawyer has repeatedly reminded us, I'm not a "legal eagle".
However, I've written quite a lot of expert witness reports, submitted to both criminal and civil courts, and worked alongside a lot of solicitors and barristers in the course of that.
My take on it is that virtually all evidence can potentially be submitted to a court, but all of that can (and probably will) be challenged for its validity, errors, intertpretation and truth.
Which to me, seems entirely appropriate.
I recently worked on a detailed analysis of a very large military fatal accident inquiry. A tiny amount was redacted - basically only the names of key serving personnel and their families, and a few items about operational codes. Certainly less than 1% of the whole, and virtually nothing that interfered with my ability to analyse the accident. My impression is that since Mull of Kintyre - which was about the first time I had detailed sight of investigations into a military accident, the MoD has changed its approach massively and has become far less overtly secretive.
G