The British Post Office scandal, also called the Horizon IT scandal, involved Post Office Limited pursuing thousands of innocent subpostmasters for shortfalls in their accounts, which had in fact been caused by faults in Horizon, accounting software developed and maintained by Fujitsu. Between 1999 and 2015, more than 900 subpostmasters were convicted of theft, fraud and false accounting based on faulty Horizon data, with about 700 of these prosecutions carried out by the Post Office. Other subpostmasters were prosecuted but not convicted, forced to cover Horizon shortfalls with their own money, or had their contracts terminated. The court cases, criminal convictions, imprisonments, loss of livelihoods and homes, debts and bankruptcies, took a heavy toll on the victims and their families, leading to stress, illness, family breakdown, and at least four suicides. In 2024, Prime Minister Rishi Sunak described the scandal as one of the greatest miscarriages of justice in British history.

Post Office Limited, commonly known as the Post Office, is a retail post office company in the United Kingdom that provides a wide range of products including postage stamps and banking to the public through its nationwide network of around 11,500 post office branches. Most of these branch post offices are run by franchise partners or by independent business people known as subpostmasters; the remaining 1% are directly managed by Post Office Limited.