Ben,
Two Pumas would have made infinitely more sense, especially in view of the importance of the pax.
I still firmly believe that someone above station level was trying to make a political statement by ordering this very important flight in this particular aircraft. The statement was probably supposed to show that the Mk2 was perfectly safe in spite of what was being said by the people that flew them, including Boscombe Down's test pilots.
It went tragically wrong and in an attempt to put a lid on this dreadful management mistake, the crew got the blame.