I found this video yesterday.
The first part in which the journalist explains the background is extremely interesting.
https://www.youtube.com/watch?v=jpkSIGd7Z68Some highlights:
- the Post Office Investigative Branch is the oldest policing organisation in the World
- sub-postmasters are not employees of the Post Office, they work under contract.
- ICL (later Fujitsu) won the contract for Horizon despite coming last in the bidding process in eight of eleven categories because they put forward an innovative contract structure in which they took most of the risk.
- The Post Office had to pay Fujitsu to investigate defects
- Fujitsu had to pay the Post Office whenever the service level agreement was breached
The last two points are important because it means neither Fujitsu nor the Post Office had any incentive to report problems to the other party.
The second part was taken up by the personal stories of two sub-postmasters. It was very hard to listen to this bit.
Then we have Q&A.
As a person who was in the bespoke software industry for many years, I found the answer to the first question very illuminating.
Fujitsu built a prototype system and demo'd it to the PO who then said it was great so roll it out. Now, the word "prototype" is used differently in the software industry as compared to manufacturing. A prototype is usually hacked together quickly to give the customer an idea of what the final system will look like. There is usually an understanding (amongst the programmers, at least) that the prototype will be thrown away and not used in production. It would be better to call a software prototype a mock up. That would be a more honest appraisal of what you have got.
Anyway, in this case the prototype was not thrown away and instead, they rolled it into production and built on it. Nick Wallis at 1:20:13 is quite wrong to say that normally everybody throws the prototype away. What Fujitsu did happens quite often. It's a recognised risk of developing prototypes. It's really hard to demonstrate a prototype to the customer and then, when they say "great, let's roll it out", tell them it'll be another six months.
Horizon was never fit for purpose and given the devastation it caused, multiple people from Fujitsu and the PO need to go to prison.