Arthur would have been precluded from jury service due a having a criminal record.
Arthur would be disqualified from being on the jury in this case, as not only does he know the defendant, but also the police officer, (Chisholm), who is appearing in the case. Failure to inform the court of these facts could leave him open to prosecution. Also he discusses the case with Chisholm outside the court building, which is against the instructions that Judges give jurors at breaks for lunch and the end of each day, while the case is being heard.
The judge uses a gavel. British (& Canadian) judges do not have gavels.