I haven't read it all, but that day of inquiry evidence on 11 October 2022, laying out the story from 1995 onwards, contains paragraph after paragraph completely damning to ICL & Fujitsu.
Eg, someone on one of these threads mentioned the fact that you can't build a decent system unless you know the client's requirements.
Here's the inquiry evidence (pp96-97):
In a report dated 18 December 1998, Project Mentors found that ICL Pathway had "made no attempt to undertake requirements analysis in accordance with normal industry practice", despite having access to the sponsors' requirements for the benefit payments service at the
time of entering into the contract.
As a result of this failure, the sponsor's expert concluded that ICL Pathway had designed and partially built a system without knowing whether it fully met the requirements of the Department of Social Security.
Project Mentors acknowledged in their report that the analysis which they had undertaken was restricted to the benefit payment service. However, they expressed "grave concerns" that the same lack of professional analysis would be apparent in other areas of the system, and articulated a particular concern about the EPOSS application. The cross-reference to that is POL00031114 at paragraphs 2.2 and 2.3.4.
Reflecting on the impact that this failure was likely to have upon the future of the programme, Project Mentors made an important observation. [...] Under its conclusion "Impacts on the Programme in the Future", Project Mentors said:
"Our experience of systems where requirements have not been analysed satisfactorily is that the system fails to meet the users' needs. An effective acceptance test will identify many such failings necessitating considerable rework. The result is a significant extension of the time and cost required to complete the system and roll it out. The alternative is to allow unacceptable processing in the operational environment, with unpredictable and potentially damaging results."
https://www.postofficehorizoninquiry.org.uk/sites/default/files/2022-10/POH%2011%20October%202022.pdf
[NB Project Mentors was an independent consulting firm hired by Post Office Counters & the Benefits Agency]