While Blue on Blue is naturally an occupational hazard of warfare, like any occupational hazard this does not mean it should therefore be accepted as inevitable. That is not missing the point but taking the real world as it is and trying to reduce the likelihood.
And if you draw the occupational hazard line to its logical conclusion then investigating the matter fully to prevent a repeat would be 'active monitoring', a major part of the Management of Successful Health and Safety guidelines as laid down by the government under which we all act.
Cold as it is persuing the H&S implications of the MoD failure to act/attempt to cover-up may be the best and most legally enforcable route to go down.