What New Zealand Organisations Can Learn from the UK’s Post Office Horizon Scandal

The UK’s Post Office Horizon scandal has been called the UK’s most widespread miscarriage of justice. Between 2000 and 2013 the UK Post Office prosecuted postmasters and others who worked in branches in England and Wales in reliance upon incorrect information from the Horizon computer system which suggested money was missing from their branch accounts.

Many hundreds of people were convicted wrongly, of criminal offences, and many thousands of people have been held responsible, wrongly, for losses that were illusory. Many sub-postmasters went to prison for false accounting and theft. Others were financially ruined. There were at least 13 suicides.

A TV drama (Mr Bates v The Post Office) fuelled anger. There is a lengthy UK inquiry. In July 2025 the inquiry released volume 1 of its report focusing on the suffering endured by sub-postmasters and their fight for compensation. The Inquiry’s final volumes are still some months away.

Lessons for New Zealand?

For New Zealand lawyers, regulators, directors, and public bodies, the Horizon scandal is more than an overseas failure. It is a cautionary example of how governance weaknesses, overconfidence in technology, and institutional blind spots can combine to produce systemic injustice.

The structural risk where the prosecution has a stake in the outcome: The UK Post Office controlled the data through the Horizon system developed and supplied by Fujitsu; the Post Office investigated disputes; and it prosecuted individuals. That concentration of power created a structural blind-spot, where challenging the system meant challenging the Post Office.

For NZ: Similar risks can arise whenever the same organisation generates evidence, investigates alleged wrongdoing and drives enforcement outcomes. Robust independence checks become increasingly important in those situations.

Expert evidence and the culture behind it: In the UK, the Horizon computer system data was treated as being correct, despite there being known bugs. The issue was technical and cultural. While the inquiry’s final report is awaited, it appears that experts were poorly instructed, there were questions over their independence, limitations were not fully disclosed, and evidence was presented with too much certainty.

For NZ: Similar risks can arise whenever prosecutions depend heavily on specialised scientific or technical evidence. While we have a Code of Conduct for expert witnesses it is only effective if experts are properly briefed and organisations are willing to disclose weaknesses.

Disclosure failures can be systematic: In the UK inquiry, criminal law expert Duncan Atkinson KC said¹ “As time passed, the number of cases where Horizon issues were being raised proliferated, and the need for cross-disclosure between them should have become all too obvious. It is far from obvious that this was carried out, however.” For NZ, cross-disclosure between cases where similar issues may arise could easily be overlooked. Prosecution agencies should ensure that they are alive to the potential need for cross-disclosure in appropriate cases.

Investigating Exculpatory Evidence: In the UK inquiry, criminal law expert Duncan Atkinson KC said² “…there was a significant period of time when, on my review of the policies, the need to investigate lines of enquiry that might exonerate the suspect was not spelt out as being necessary. It is difficult, therefore, to conclude at the policy level that such a requirement was recognised or undertaken.”

In NZ, the Chief High Court Judge has been identified this issue. A 2023 Practice Note³ includes “Investigators must pursue all reasonable lines of inquiry, whether inculpatory or exculpatory in respect of a suspect.” A challenge is the extent that such thinking becomes part of prosecution practice and culture.

The Danger of Defending Earlier Decisions: The scandal demonstrates the danger of organisations becoming invested in defending earlier decisions. Once substantial resources, reputations and institutional positions are committed, there can be a tendency to treat challenges as threats rather than opportunities to identify error. Effective governance requires mechanisms that encourage reconsideration of assumptions when credible concerns arise repeatedly.

The importance of listening to repeated complaints: One feature of the scandal was the persistence with which affected postmasters raised concerns over many years. When organisations receive repeated complaints raising similar issues, the question should not simply be whether each complaint can be answered individually. There should also be consideration of whether the pattern itself indicates a systemic problem requiring independent review.

Privilege and Conduct under Scrutiny: In the UK inquiry, some lawyers that acted for the Post Office in the past, gave evidence and were questioned on their approach. Privilege did not protect the communications in issue. Further, the Solicitors Regulation Authority has more than 20 live investigations into solicitors and law firms linked to this scandal, including those who were working on behalf of the Post Office/Royal Mail Group.⁴ The Metropolitan Police’s Operation Olympos investigation is examining potential criminal offences connected with the scandal.

For NZ: privilege can be disallowed if it is necessary to enable the defendant in a criminal proceeding to present an effective defence (s67(2) Evidence Act 2006) and can be waived by clients. For lawyers involved in contentious matters, the inquiry is a reminder that legal advice may ultimately come under scrutiny. It is worth considering whether the advice and conduct would withstand public or regulatory examination if privilege were later waived or displaced.

Unsafe guilty pleas are a real risk: In the UK, convictions were quashed of people who had pleaded guilty, despite the Horizon’s evidence later being found unreliable. In NZ, this illustrates a risk if our system relies too much on plea bargaining arrangements. Innocent people may plead guilty to avoid serious sentences.

The challenges for redress schemes: The Inquiry commented⁵ that the approach of the Post Office’s lawyers “and, by extension, the Post Office, to the assessment of offers is too legalistic and fails, too often to give the postmaster the benefit of the doubt.” In NZ: when an injustice has been done, it is important that any redress scheme is fair and tries to avoid being too legalistic.

Governance failures at the top: At its core, Horizon was not merely a technology failure. It was a governance failure. Senior decision-makers were repeatedly presented with warning signs but failed to ask sufficiently challenging questions. Effective governance requires a willingness to test assumptions, encourage dissenting views, and distinguish between protecting an organisation's reputation and identifying the truth. Those lessons apply equally to public bodies, regulators, listed companies and professional organisations in New Zealand.

Conclusion

The Horizon scandal demonstrates that technology rarely causes injustice on its own. The greater risk arises when institutions become unwilling to question their systems, assumptions or past decisions. For New Zealand organisations, the lesson is clear: governance, disclosure and investigative processes must be robust enough to identify error before it becomes systematic. Once confidence in a system replaces scrutiny, the consequences can be profound.