Interesting times and one that really needs guidance for the future to stop one public body chasing another public body with all the waste of time and resources it entails.
Sadly nobody seems willing / able to grasp the nettle.
Ultimately quite rightly the AAIB are the lead in the accident investigation but of course the coroner has a variety of verdicts to be considered and so whilst AAIB reports are great start / middle and end to the facts of the matter the objectives of the AAIB and coroner are not the same.
This leads to an awkward and damaging situation if as a result of matters arising that require a prosecution the quality of the AAIB's conclusion potentially gets questioned in open court by others.
All the while average Joe Blow and any victims just see cans get kicked and an odd and lengthy situation develop.