Airpolice,
I entirely agree with you that a close examination of flight logs could provide useful contextual material. Just as obviously, so could ANYTHING which was said on ANY radio during the latter stages of this flight. Your suggestion that Police Scotland and AAIB are entitled to withhold it on grounds of relevance ( or for that matter any other grounds) is ridiculous, not least as particulars of radio traffic earlier in the flight are included, when they are patently irrelevant.
Look at the radar trace again, look at the detour, and ask yourself whether it was likely a pilot low on fuel would have undertaken it on a whim, and without some form of external input or communication.