I once worked with a former member of the Vickers flight test department who was there when these fateful events took place. He told me the following which is not in the report;-
Lithgow had picked up some unexpected stall behaviour on early test flights which he felt wouldn’t meet certification requirements. One of the proposed solution was to revise the wing to fuselage incidence which had massive implications for the whole program so was hotly debated. In an effort to make a decision, against impossible time pressures, the assistance Head of Aerodynamics and Design were cleared for a test flight so that decisions could be made on the spot to expand the stalling envelope. My colleague heard the flight test voice recordings;- he said that the during the initial stalls, the two engineers were on the flight deck and could be heard encouraging Lithgow to go a little further in the hope of completing the full BCAR stall demonstration. Ultimately, although close, tragically it was step too far. After this incident company regulations/procedures were changed such that heads of engineering were not allowed to fly on high risk test flights. This was to put an end to ad hoc/peer pressure during flight tests.