In our previous blog post, we did our best to summarize the facts of one of the biggest scandals in the history of the British justice system. In this post, we analyze the Great Post Office Scandal through the lens of behavioral ethics in an attempt to engage in a little informed speculation as to why this moral tragedy occurred.

Behavioral ethics (see video at is the science of moral decision making. Derived from research in such fields as behavioral psychology, cognitive science, evolutionary biology, primatology and others, it studies how and why people make the ethical and unethical decisions that they do. Nick Wallis’s detailed depiction of this scandal—The Great Post Office Scandal: The Fight to Expose a Multimillion Pound IT Disaster Which Put Innocent People in Jail—describes a sufficient number of manifestations of key behavioral ethics concepts to serve as a textbook for an entire course in the subject.

The essence of the scandal lies in the Post Office’s executives, auditors, investigators and lawyers taking the uncompromising but erroneous position that Fujitsu’s Horizon computer system that it implemented in 2000 was flawless and that if any disparities appeared on any local office’s computer terminals, well, it must have been the fault of the local Subpostmaster who, by the terms of the lengthy and opaque contract with the Post Office, was legally responsible to make up any such deficit. More than 3,500 Subpostmasters were forced to pay money that they didn’t owe to make up illusory deficits caused by Horizon’s flaws. Around 2,000 of those were fired. And more than 700 were criminally charged. Many were convicted and many went to prison.

As evidence accumulated that there were problems with the Horizon system, the Post Office hid that evidence. When Post Office auditors and investigators looked into individual cases, they refused to seriously attempt to look for the truth, invoking the company line that Horizon was flawless even though they had to know better. When Post Office executives received reports from their own consultants as to Horizon’s failings, they buried them. When sued, the Post Office executives stonewalled, sandbagged, lied, hid exculpatory information that Subpostmaster defendants were legally entitled to see, filed frivolous motions and appeals, and generally counted on the Post Office’s deep pockets to outlast the Subpostmasters’ financial resources.

Why? Why would all these folks throw morality out the window in an attempt to protect the corporate bastion? The question is particularly thorny because through much of the relevant time, the Post Office’s CEO was Paula Vennells, who was also an Anglican priest!

Initially, it’s important to note that the government was intensely pressuring the Post Office to greatly improve its financial posture and achieve profitability by 2020. When the Post Office spent a billion dollars to implement the Horizon system that other government agencies had rejected, it was doubling down. Its partner, Fujitsu, was also in financial straits in the UK and really needed this huge contract with the Post Office.

Thus, once they had made the controversial, high stakes decision to roll out Horizon, the Post Office, Fujitsu, and their executives really wanted and really needed things to go well. Because of the self-serving bias (see video at, employees of these organizations would tend to seek out, process, and even remember information in a self-serving way. Evidence that indicated Horizon’s supposed robustness would be clasped to their bosoms pursuant to the confirmation bias (see —the tendency people have to seek out information that supports the views they already hold and to interpret new evidence so as to support those views. Contrary evidence would be discounted if not ignored altogether. These cognitive tendencies would all be bolstereded by the fact that the Post Office could use money recovered from the Subpostmasters to fill holes in the Post Office’s own coffers, reinforcing this self-serving bias.

This was a win-win, but only for the Post Office. But in this time frame, fixing the Post Office’s finances was “the relentless focus” under CEO Paula Vennells. (Wallis, p. 181). The decisions people make have everything to do with what is in their frame of reference when they make those decisions. This is the behavioral concept of framing (see If your entire focus is on making a profit and ethics is excluded, you are going to make poor moral choices, as Professor Jennings explained in her book The Seven Signs of Ethical Collapse, and as the Post Office proved in this case.

Once the Post Office and Fujitsu had made public statements about Horizon’s supposed perfection and the false “alternative fact” that Fujitsu did not have the ability to unilaterally make secret changes to individual Substation Horizon systems, it would have been especially painful for them to process, accept, and especially to admit to contrary evidence. The concept of cognitive dissonance (see, which is the discomfort people feel when they hold two contradictory ideas in their mind at the same time, would likely have helped convince these employees to discount any evidence that undermined the party line.

The party line at both the Post Office and Fujitsu was that the Horizon system was nearly perfect and could not possibly be responsible for all of the discrepancies that were leading to prosecutions all over the country in numbers that were multiples of any ever seen before. Because employees could be punished for disputing the party line, they had a self-serving interest in adopting, believing, and spouting it. A very large percentage of Post Office employees were “lifers” who strongly identified with the Post Office which was, at that time at least, a respected and even beloved institution. Because of role morality (see, people often feel they have permission to harm others in ways that would be wrong if it were not for the role they are playing. In their role as loyal employees of the Post Office, the auditors and inspectors who rode roughshod over Subpostmasters may well have felt that their actions were well justified. The auditors did not do real audits and the inspectors did not do real investigations. It was not only easier for them to not seek the truth, this also eliminated any risk of reaching conclusions that were contrary to their employer’s official position.

Furthermore, when individual Post Office and Fujitsu employees were in very strong terms told to follow the party line, the influence of obedience to authority (see, the tendency people have to follow the instructions of authority figures, would have inclined them to adopt and adhere to the “Horizon is flawless” narrative.

Furthermore, these employees, like all of us, would have been subject to the conformity bias (see, the tendency people have to take cues for proper behavior from the actions of our peers. Wallis reports employees who told him that when evidence of Horizon’s flaws came up in Post Office meetings, it became clear that discussing it was verboten. “Bringing it up was not the done thing,” one employee later said. There was a “cultural blindness.” (Wallis, p. 181)

All of this would be reinforced by the in-group/out-group bias (see, the tendency people have to judge people who are like them more favorably than those who are not. Passages in Wallis’s book report that employees of the Post Office, such as executives, auditors, and investigators, looked down on the independent Subpostmasters as unqualified, lazy numpties who were “all on the take.” One of Wallis’s sources inside the Post Office believed that holding this low opinion of the Subpostmasters gave the Post Office employees “permission to believe what they needed to carry on in the way they did.” (Wallis, p. 195)

Now you might think that burying reports, shredding documents, and lying under oath would have given some of these Post Office employees pause, but remember that in their minds they were good folks. Therefore, the overconfidence bias (see, pursuant to which most of us believe that we are more ethical people than we actually are, no doubt had an impact. These employees were convinced that they were good people and therefore that the things they were doing were ethical because they were the people who were doing them. This personal overconfidence was undoubtedly reinforced by the employees’ belief in their employer. As Wallis reports: “There were plenty of people in the organization whose identity was bound up in the Post Office’s own self-image. They saw the Post Office as virtuous, so they were virtuous for working at the Post Office.” (Wallis, p. 181) Studies show that the overconfidence bias is especially problematic for people for whom an ethical self-image is especially important, such as Anglican priests.

Obviously, this analysis contains a fair amount of speculation. But it is highly likely that it also contains substantial explanatory power for how this tremendous miscarriage of justice occurred.




Cara Biasucci and Robert Prentice, Behavioral Ethics in Practice: Why We Sometimes Make the Wrong Decisions (2021).

Marianne Jennings, The Seven Signs of Ethical Collapse: How to Spot Moral Meltdown in Companies…Before It’s Too Late (2006).

Daniel Kahneman, Thinking, Fast and Slow (2011).

Robert Prentice, “The Case of the Irrational Auditor: A Behavioral Insight into Securities Fraud Litigation,” Northwestern University Law Review 95: 133-219 (2000).

Nick Wallis, The Great Post Office Scandal: The Fight to Expose a Multimillion Pound IT Disaster Which Put Innocent People in Jail (2022 Paperback edition).

Nuala Walsh, “What the British Post Office Scandal Can Teach Every Leader,” Inc. (Jan. 26, 2024), at



Behavioral Ethics:

Cognitive Dissonance:

Confirmation Bias:

Conformity Bias:


In-group/Out-group bias:

Obedience to Authority:

Overconfidence Bias:

Role Morality:

Self-serving Bias: