"A layman might well wonder why the function of a court in cases such as these should not simply to conduct an inquiry into the question whether the tribunal was in fact biased. After all it is alleged that, for example, a justice or a juryman was biased, ie that he was motivated by a desire unfairly to favour one side or to disfavour the other. Why does the court not simply decide whether that was in fact the case? The answer, as always, is that it is more complicated than that. First of all, there are difficulties about exploring the actual state of mind of a justice or juryman. In the case of both, such an inquiry has been thought to be undesirable; and, in the case of juryman in particular there has long been an inhibition against, so to speak, entering the jury room and finding out what any particular juryman actually thought at the time of decision. But there is also the simple fact that bias is such an insidious thing that, even though a person may in good faith believe that he was acting impartially, his mind may unconsciously be affected by bias - a point stressed by Devlin LJ in R v. Barnsley County Borough Licensing Justices , ex parte Barnsley and District Licensed Victuallers Association[1960] 2 All ER 703 at 715,[1960] 2 QB 167 at 187. In any event, there is an overriding public interest that there should be confidence in the integrity of the administration of justice, which is always associated with the statement of Lord Hewart CJ in R v. Sussex Justices , ex parte McCarthy[1924] 1 KB 256 at 259 ... that it is -
"In conclusion, I wish to express my understanding of the law as follows. I think it possible, and desirable, that the same test should be applicable in all cases of apparent bias, whether concerned with justices or members of other inferior tribunals, or with jurors, or with arbitrators. Likewise, I consider that, in cases concerned with jurors, the same test should be applied by a judge to whose attention the possibility of bias on the part of a juror has been drawn in the course of trial, and by the Court of Appeal when it considers such a question on appeal. Furthermore, I think it unnecessary, in formulating the appropriate test, to require that the court should look at the matter through the eyes of a reasonable man, because the court in cases such as these personifies the reasonable man; and in any event the court has first to ascertain the relevant circumstances from the available evidence, knowledge of which would not necessarily be available to an observer in court at the relevant time. Finally, for the avoidance of doubt, I prefer to state the test in terms of real danger rather than real likelihood, to ensure that the court is thinking in terms of possibility rather than probability of bias. Accordingly, having ascertained the relevant circumstances, the court should ask itself whether, having regard to those circumstances, there was a real danger of bias on the part of the relevant member of the tribunal in question, in the sense that he might unfairly regard (or have unfairly regarded) with favour or disfavour, the case of a party to the issue under consideration by him; though, in a case concerned with bias on the part of magistrates' clerk, the court should go on to consider whether the clerk has been invited to give the magistrates advice and, if so, whether it should infer that there was a real danger of the clerk's bias having infected the views of the magistrates adversely to the applicant."
"It is because the court in the majority of cases does not inquire whether actual bias exists that the maxim that justice must not only be done but be seen to be done applies. When considering whether there is a real danger of injustice, the court gives effect to the maxim, but does so by examining all the material available and giving its conclusion on that material. If the court having done so is satisfied that there is no danger of the alleged bias having created injustice, then the application to quash the decision should be dismissed. ..."