@tomoyo @Em0nM4stodon Horizon was the Post Office, not Royal Mail, and even today the Post Office is attached to the Department of Business and Trade even if it's not longer a department in it's own right.
For that matter Horizon began before Royal Mail was separated and privatised.
Btw what the Post Office did, for the majority of cases, was be a private prosecutor, which is just a regular thing in English law, anyone with enough time/money can do it, there are random people right now using it to seek justice when the CPS doesn't want to, or even attempting to bring war-crimes charges against citizens who've gone to fight in other countries ‘wars’.
The danger wasn't so much that they had a special privilege, it's that they had a well funded legal department lacking in any ethics, helped along of course by Legal Aid not being fit for purpose, denying people a proper defence.