Barnwood
I am no longer in the BoI world. However, I recall that when the rules changed so that BOIs were not permitted to apportion blame we went to great lengths to ensure that none was inferred. This was quite difficult to do especially when it was clear that someone (or indeed some people had made mistakes - which do happen). To the extent that (I am trying hard to give an fictional example that does not give away any details of BoIs I may have been involved with for obvious reasons but it does make the example seem too simplistic) if a pilot had failed to remove an item in preflight checks the BOI would not say that 'Flt Lt Prune failed to to remove' said item but would relate the fact that it 'had not been removed' (obviously if there is only one pilot and it is his job then...). That was back in about '98-99 ish.
I have subsequently been a member of a BoI investigating a fatal incident and we went to extraordinary lengths (under direction from P-staff and lawyers) in phrasing our findings so that it did not apportion blame to individuals but just stated the facts.
So where does this lead us. I am loathed to comment specifically about this case because (like the majority on here) I know very little about it apart from second hand accounts. Now the 'high price help' have often gone off message; however, I am sure that what they wrote would have been checked before it was finalized. The issue appears to be whether it is factual to say that ATC instruction was unsafe. I note that neither author states that xxxx[the controller] gave an unsafe instruction; accordingly, they do not actually say that it was his fault. So any challenge to the statement must concentrate on factual accuracy.
As for vicarious liability, the MOD could be vicarious liable irrespective of any blame apportionment that may have occurred in the BOI. Such liability has been interpreted by the courts extremely widely. As an unrelated (obviously) example of how wide the courts can extend its cover:
In an after work drink session in a local pub a police officer was deemed to have sexually harassed a female police officer. Neither were on-duty. However, that court decided that the Chief Constable of their force was vicariously liable for the male officer’s actions - unlucky!