Any accident scene is a potential crime scene and therefore the police have primacy, even on-base. As far as I know they always have done.
Just to put that one to rest we need to define "Always". Let me provide two data points. One: In April 1983, I was part of a BoI investigating a JP crash at Elvington. We never saw a policeman from beginning to end. Had we suspected a crime, e.g. sabotage, we would have asked for an RAFP investigation. If that sabotage looked like attempted murder, we'd have passed that aspect of it to the civil police. Neither was the case, and there was NO police involvement.
Data Point 2. Last year's Red Arrows ground ejection investigation was, I understand, delayed while the BoI waited for the Civ Police to release the seat to them. What the police would have made of an ejection seat I cannot imagine, but that's when I first learnt about "Police Primacy".
Now, between those two dates something changed. The organisation of the RAF has changed out of all recognition in that time, I know. So I repeat my original question. When and Why did this "Police Primacy" phenomenon occur?
Walter Kennedy's helpful contribution indicates it was subsequent to the MoK Chinook, which sounds right. Was that accident the catalyst for the change, or was there something else?