I'm not sure what your link was trying to say, Dr. Bill, and anyway it's based on USn Law. Osborn's Concise Law Dictionary says this:

nisi prius A trial at nisi prius was a trial by a jury before a single judge, either at the sittings held for that purpose in London and Middlesex, or at the assizes. Formerly all common law actions were tried at the bar, that is, before the full court, consisting of several judges; and, therefore, the writ for summoning the jury commanded the sheriff to bring the jurors from the county where the cause of action arose to the court at Westminster. But when the statute 13 Edw. 1 directed the justices of assize to try issues in the county where they arose, the sheriff was thenceforth commanded to bring the jurors to Westminster on a certain day, "unless before that day" (nisi prius) the justices of assize came into the county.

Bingley

Bingley