At the end of the trial, the judge bangs a gavel. Gavels have never been used on English courts.
The bird seen while Penance is washing, described as a redwing, is actually a red-winged blackbird, an American species which has never been seen in London and only ever been seen in the UK once (Orkney 2017)
Judge: After five weeks... five grueling weeks of testimony as to your heinous and unrepentant malfeasance... Malfeasance is defined as "the performance by a 'Public Official' of an act that is legally unjustified, harmful, or contrary to law; wrongdoing (used especially of an act in violation of a public trust)." Maladie is not nor was not a 'Public Official' and is not subject to malfeasance.
The series is set in the Victorian Era (1837-1901) and frequently mentions Britain "being at war," which narrows it down to the period of the Crimean War (1853-1856).
In the scene with Lord Swann coming out of the Inspector's office, he pulls out, lights, and then shares a cigarette with the female reporter. In the close-up shot, the cigarette clearly has a filter at its end, a feature that was not added to cigarettes until 1950.