UK law said that there was a presumption that computer systems were working correctly unless there was evidence to the contrary. That’s not inherently nuts. It makes roughly as much sense as assuming that, say, a dishwasher is in working order unless there’s evidence to the contrary. This presumption in and of itself could just as well aid a person’s defense as hinder it (e.g. if they have an alibi based on computer records).

In this case it should have been very easy to provide evidence to override the presumption that the Horizon system was working correctly. That this didn’t happen seems to have resulted from a combination of bad lawyering and shameless mendacity on the part of Fujitsu and the Post Office.

Don’t get me wrong — the whole thing is a giant scandal. I’m just not sure if this particular presumption of UK law is the appropriate scapegoat.