What happened
Horizon was installed by Fujitsu from 1999 as part of a £1 billion government contract. Almost immediately, subpostmasters began reporting unexplained shortfalls. When they raised concerns with the Post Office, they were told the system was infallible and the problem must be their error or dishonesty.
The Post Office pursued prosecutions knowing: 1. Hundreds of subpostmasters were reporting identical unexplained discrepancies 2. Internal Fujitsu bug reports documented serious software errors 3. Their own legal teams had received disclosures about system bugs that were not passed to defendants
The cover-up was active. The Post Office withheld evidence from defendants. It used its unique status as a private prosecutor — one of the only private organisations in England with the right to prosecute without the CPS — to pursue cases that should never have reached court.
The public became aware largely through an ITV drama ('Mr Bates vs The Post Office') broadcast in January 2024. Within days of broadcast, Sunak announced emergency legislation to quash convictions. The inquiry, which reported in 2024, found the Post Office had been 'dishonest' and 'callous' and called for criminal prosecutions of Post Office executives.
The Government was implicated as majority shareholder: ministers received warnings that did not trigger action. Horizon's problems were raised in Parliament by MPs from 2010 onwards.