Shortly after we see a notice of the scheduled hanging, dated 1908, the hangman remarks, "Even my lamented master, the great Mr Berry himself, never had the privilege of hanging a duke." He presumably means James Berry who died in 1913.
The first murder that Louis Mazzini commits involves him swimming fully dressed underwater to release a boat from its moorings. In spite of having brought no change of clothes or even a towel, he is shown shortly after committing the murder paddling down the river with his clothes bone dry.
When "The Hangman" (Miles Malleson) opens the peep-hole to the prisoner's cell, he moves the covering to the right, with a finger. After we are allowed to gaze at the back of the prisoner's neck for a few seconds, the shot reverts to the outside of the cell door; The Hangman releases the cover which closes from left to right, not right to left, as it should have done.