According to the TV drama, the Fujitsu staff could go in and change data in the live data, while the log said it was the subpostmaster making the change. If so, that seems like negligently bad design.
From memory:
UK Covid test and trace system: £37 billion pretty much wasted
UK NHS IT system: £12 billion pretty much wasted
And I'm sure there are lots of others.
And yet we are still giving huge projects to the same companies. Amazingly, Fujitsu's contract for the Horizons system has recently been renewed.