Chaps,
There are 2 distinct aspects to this whole sorry business:
1. There was insufficient cause for Wratten and Day to pin their finding of Gross Negligence on the 2 pilots.
2. Various senior people allegedly ran roughshod over their own airworthiness regulations whilst trying to bring the HC2 into service.
Now, one might consider that 2 may well have been instrumental in the accident, but most folk simply accept that confirmation of 1 is the more important. An independent judicial inquiry should resolve 1 fairly quickly, but would probably then lead to an in-depth investigation of 2 as more and more stones are turned over.
I feel strongly that 1 should be settled first - and quickly. Then 2 can be considered at length - but assuredly not just by some internal MoD inquiry.