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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →On 16 November 2022, David McDonnell told the Post Office Horizon IT Inquiry that the team developing Horizon’s Electronic Point of Sale Service (EPOSS, also called EPOS) was known inside ICL Pathway as “the joke of the building”. He described a “Wild West” working environment, weak engineering controls and persistent defects. His evidence was a witness account—not a judicial finding that every developer was incompetent or that one team caused the entire Horizon scandal.
What Horizon and EPOSS were
Horizon was the Post Office’s branch computer system. EPOSS/EPOS was a component within that programme, handling electronic point-of-sale functions and cash-accounting work used when branches balanced their accounts. ICL Pathway developed the system; Fujitsu owned ICL and supplied the technology.
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That distinction matters. “EPOSS software” was not a separate consumer product. The evidence concerned a subsystem whose data could affect the figures subpostmasters were expected to reconcile.
For background on the terminology and the inquiry evidence, see the contemporary Computer Weekly report and McDonnell’s official witness statement.
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Who made the “joke of the building” remark?
McDonnell joined ICL Pathway in 1998 and initially worked as deputy development manager on the Horizon EPOSS development team. He later joined a task force examining problems in the system and co-authored a report on its findings. His testimony was heard during Phase 2 of the statutory inquiry, which examined Horizon’s procurement, design, development, testing and rollout.
In the inquiry transcript, McDonnell said the EPOSS team’s reputation was widely understood within the organisation. The phrase was his description of that reputation, not an official company classification or a conclusion by the inquiry.
What McDonnell said was wrong with the team
Uneven capability, not a claim about every developer
McDonnell said that, in his assessment, only some of the roughly eight-person team were capable of producing professional code. He also acknowledged that some colleagues were good and that others were usable but mediocre. The evidence therefore supports a criticism of capability and management, not a blanket assertion that every team member lacked qualifications.
Weak development controls
According to his witness statement and oral evidence, the team lacked the controls normally used to make complex financial software dependable:
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- no meaningful, consistently applied development standards;
- no dependable methodology or organisational structure;
- insufficient design documentation and sign-off;
- weak or absent peer-review and unit-testing practices; and
- poor discipline in how code and defects were managed.
He characterised the culture as operating like the “Wild West”. Those are allegations and recollections from one witness, even though they were given under oath and are part of the inquiry’s evidence.
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Persistent and increasing defects
McDonnell used the volume and persistence of internal problem or defect records—referred to in the transcript as PinICLs—as an indicator of the software’s condition. He said the number was striking for a project of Horizon’s size and was not falling as the system matured. In his account, new defects continued to appear and became more complex rather than diminishing.
That is different from saying that any large software project will contain no bugs. The concern was the reported level, persistence and governance of the defects, and whether the team had a credible way to bring them under control.
What the EPOSS task-force report added
An internal task force investigated EPOSS problems. McDonnell identified its report as Report on the EPOSS PinICL Task Force, reference IA/REP/008, linked in his statement to inquiry document FUJ00080690. The account of the report included a conclusion that the author of some code showed no understanding of basic mathematics or elementary programming rules.
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The proposed rewrite of the cash-account component
McDonnell said the critical cash-account software should have been rewritten. He argued that the work could be done incrementally rather than treating Horizon as an indivisible block. He said he raised the issue with former Fujitsu chief architect Gareth Jenkins but could not obtain support for the rewrite. During a later restructure, McDonnell said he was offered a leadership role and made a fix to the cash-account software a condition of accepting it; he said the discussion then ended.
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A rewrite is not automatically safe or cheap. Replacing a core accounting component in a live nationwide system can introduce new defects and disrupt operations. Keeping known defective code, however, preserves technical debt and operational risk. The important question was whether management had an adequate, evidence-based remediation plan—not whether rewriting is always the right engineering answer.
How widely were the problems allegedly known?
McDonnell said the team’s reputation was known among testing staff and, in his recollection, reached senior levels. He also said Fujitsu sent three coders from Japan to audit the situation.
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Why EPOSS mattered to subpostmasters
The potential significance was practical. Horizon recorded branch transactions and balances; some subpostmasters later reported unexplained shortfalls. The Post Office treated many discrepancies as evidence that the branch operator owed money or had committed an offence. Some people repaid sums, faced prosecution or were imprisoned. Later litigation and inquiry evidence exposed serious problems with Horizon and with the way its data was investigated and presented.
The testimony does not establish that every shortfall, prosecution or conviction resulted from one EPOSS coding defect. A coding error, a defect that changes transaction data, a system-generated discrepancy, a human accounting mistake and a prosecution based on incomplete computer evidence are different propositions. The wider scandal also involved architecture, connectivity, testing, disclosure, governance and investigative practice. A broader overview is available from Computer Weekly’s Horizon explainer.
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What this evidence does—and does not—prove
- It does show: McDonnell reported serious weaknesses in EPOSS staffing, process controls, documentation, testing and defect management.
- It does show: an internal task force examined EPOSS problems and a rewrite of the cash-account component was proposed, according to his evidence.
- It does not show: that all developers were unqualified or that every Horizon function was defective.
- It does not show: the precise cause of an individual branch discrepancy or the conclusions of the reported Japanese audit.
- It does not show: that poor development practice alone explains every unsafe prosecution or later legal finding.
Later inquiry work also examined the reliability of Horizon data and the institutional decisions surrounding it. For comparative context, see reporting on the inquiry’s expert IT evidence: Computer Weekly.
Key dates
| Date | Event |
|---|---|
| 1998 | McDonnell joined ICL Pathway and worked on the EPOSS development team. |
| 1998–1999 | Development and testing concerns described in the contemporary account and McDonnell’s evidence. |
| 1999 | Horizon rollout to Post Office branches began, according to the contemporary report. |
| 16 November 2022 | McDonnell gave evidence to the statutory Post Office Horizon IT Inquiry. |
The inquiry transcript for the hearing is available at the official inquiry site. The evidence is historical testimony from 2022, not a new 2026 revelation.
Frequently Asked Questions
Did the inquiry rule that the EPOSS team was incompetent?
No. “The joke of the building” was David McDonnell’s description. He gave evidence about uneven capability and weak processes; it was not a judicial finding about every team member.
Was EPOSS the whole Horizon system?
No. EPOSS/EPOS was a point-of-sale and cash-accounting component within the wider Horizon programme.
Did one software bug cause all the wrongful prosecutions?
The evidence does not support that single-cause claim. Technical defects formed part of a wider chain that included testing, governance, disclosure and prosecution practices.
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The Bottom Line
McDonnell’s “joke of the building” description mattered because it connected Horizon’s later human consequences to reported weaknesses in the EPOSS development process. It is important evidence of an alleged governance failure, but not a complete explanation of the Horizon scandal or a substitute for the inquiry’s wider findings.
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