Horizon is an EPOS and back-end finance system for thousands of Post Office branches around the UK, first implemented by ICL, a UK technology company later bought by Fujitsu.

Soon after its installation, branch managers realized the system was faulty. The software regularly showed that money — often many thousands of pounds — had gone missing from Post Office accounts.

The Post Office’s former senior criminal lawyer, Jarnail Singh, described his team’s success as destroying the defence’s arguments against the Post Office Horizon accounting software.

According to the Licensed Post Office Group, which represents the interests of about one-third of the 2800 licensees operating under Australia Post’s franchise model, the new system is causing a ...