In Designers Guild Ltd v. Russell Williams (Textiles) Ltd,2 the House of Lords held that the Court of Appeal had erred by assessing anew the decision of the trial judge as to the substantiality of the defendant’s copying of the plaintiff’s fabric and wallpaper designs. As Lord Hoffmann explained, because that decision involved “the application of a not altogether precise legal standard to a combination of features of varying importance,” analysis of substantial copying “falls within the class of case in which an appellate court should not reverse a judge’s decision unless [the judge] has erred in principle.”3 Their Lordships agreed that there had been no such error. The New Zealand Supreme Court endorsed this approach in 2006. Citing Designers Guild, it said: “[I]t is appropriate for appellate Courts to give the trial judge’s assessment the degree of latitude that conventionally applies to appellate review of a discretion.”4