Fujitsu UK, a major information and communications technology (ICT) provider, has played a pivotal yet largely invisible role within the UK’s public infrastructure. Their systems underpin critical services—banking, transport, government operations, and, most fatefully, the national Post Office. The company’s legacy, stretching from its 1935 Japanese roots to its acquisition of ICL in 1990, granted it unprecedented influence over British digital systems. The core event that shattered public trust was the Post Office Horizon scandal. Beginning in 1999, the Post Office deployed Horizon, an accounting system developed and maintained by Fujitsu UK. Rather than simplifying finances, Horizon introduced unexplained discrepancies—apparent cash shortfalls in local post office branches. Over 900 sub-postmasters and sub-postmistresses, the lifeblood of rural and urban communities, were prosecuted for theft, fraud, and false accounting, when in fact software bugs were to blame. Despite persistent reports from affected staff about system errors, the Post Office maintained absolute faith in Horizon’s reliability, often dismissing user complaints as dishonest cover stories. Public inquiry later revealed that not only did Fujitsu know of significant bugs and faults as early as 1999, but evidence of these defects was actively concealed during legal proceedings. In court, the Post Office and Fujitsu representatives depicted Horizon as robust, misleading tribunals and enabling a miscarriage of justice on an unprecedented scale. The scientific and organizational failure was profound: a single, faulty technology error propagated across hundreds of branches, while institutional structures—legal, corporate, governmental—failed to apply necessary oversight or skepticism. The ethical failings were equally severe. Innocent individuals were coerced into confessions, bankrupted, imprisoned, and ostracized from their communities. The human cost—mental health crises, family breakdowns, and even deaths—was catastrophic and long-lasting. Public awareness of this injustice grew slowly. First, Computer Weekly exposed the issue in 2009; then further legal action, driven by the Justice for Subpostmasters Alliance, secured compensation and sought to clear names. By 2024, over 100 wrongful convictions had been overturned, with thousands more recognized as victims. £1 billion in government compensation is expected, and emergency legislation aims to rapidly exonerate those wronged. Fujitsu UK’s systemic role in public services remains significant. They continue to hold billions in government contracts across departments such as Defence, Energy, HMRC, and Health. Issues with other major projects, such as a failed NHS digitalization initiative, have highlighted the risks of dominant IT suppliers and the difficulty of contract termination. Even in the aftermath of the scandal, Fujitsu has won new government contracts and continues to supply critical systems. This episode has prompted demands for greater regulatory oversight, rigorous auditing of technology in public services, and more robust mechanisms for whistleblowing and redress. It has heightened awareness of the frailty of digital trust—how IT errors, left unchecked and undisclosed, can cascade into national tragedies. The Post Office Horizon scandal’s legacy endures as a cautionary tale about the power and peril of digital infrastructure. It serves as a stark reminder: the systems shaping society must be transparent, accountable, and subject to constant scrutiny, lest their failings devastate the very people they were meant to serve.