I get that the investigators, lawyers and lower-level managers were being encouraged with bonuses to cover-up the Horizon shortcomings, and use settlement offers to browbeat subpostmasters into exhonerating Horizon.

What I haven't learned yet, is why senior management wanted so much to exhonerate Horizon, that they would hand out bonuses to investigators, and to inquiry witnesses who gave "the right" testimony. The Post Office doesn't have a lot of money; it only broke profit in about 2014.

It can't be that the senior management were responsible for commissioning it, and screwed up; most of the people who did the comissioning will have retired. Similarly, the system was comissioned under a Labour government, and nobody from that era is still around. So I suspect it's the civil service, whose policies and cultures can outlive any human.