What is the test for bringing forward a charge before the Court of Appeal?

The Appellant brought forward the case of The King v. Sussex Justices 1924 1 K.B. 256 for the well known proposition that justice must not only be done, “but should manifestly and undoubtedly be seen to be done”. In that case, a deputy clerk who sat with the justices during their deliberations, was also a member of the firm of solicitors engaged in the civil proceedings for damages against the applicant in respect to the same collision as giving rise to the charge being considered.