DV. Spot on.
MAA and AAIB investigators/panel members have very different roles. Even if trained in the same way, the MAA people do not have to apply that training in the same way.
The 2011 Red Arrows case showed up once and for all how lacking MoD investigations are. In a way their errors and mistakes were excusable, as none would have been trained in the necessary disciplines. But they didn't ask those who were. Otherwise, how could they miss that the ejection seat was not permitted in the aircraft? A first year apprentice would be crucified if he couldn't see that.
MoD and HSE then lied. The only question is whether the latter lied under oath.