The substantive right to a fair trial must be distinguished from its procedural correlatives such as the right to confront witnesses and to present a defence. The procedural rights may be subject to balancing against competing rights, but the substantive right to a fair trial is regarded as absolute in some jurisdictions.
The Supreme Court of Canada has recently not distinguished procedural fairness from substantive fairness, and by a majority it has treated the apparently composite right to a fair trial as something that can be balanced against competing rights: R v NS, 2012 SCC 72 (20 December 2012).
The implications of the case extend far beyond its facts, which raised the issue of how a court should decide whether to permit a witness to wear a niqab (face covering). There is obviously a range of potential answers: always permit it (Abella J), never permit it (LeBel and Rothstein JJ), and sometimes permit it (McLachlin CJ, Deschamps, Fish and Cromwell JJ).
The majority held that if a right competed with the defendant's righs to confront witnesses and to present a defence, and if there was no way to give full effect to all these rights, there would then be a balancing. This would require some limitation of rights, perhaps but not necessarily on both sides.
In including the substantive fair trial right in this balancing exercise the majority have declined the opportunity to use it as the ultimate criterion. Contrasting views of the importance of substantive fairness are found in cases from other jurisdictions, not considered in this case: R v A (No 2)  UKHL 25,  1 AC 45 (HL) (mentioned here on 4 September 2004, and see also the discussion of Randall v R (Cayman Islands)  UKPC 19 and of other relevant cases here on 16 September 2010, R v Davis  UKHL 36 noted here as the second entry for 19 June 2008, and the still-obscure position in Gäfgen v Germany  ECHR 759 noted here on 25 June 2010.
NS appears to establish that in Canada the right to a substantively fair hearing is not absolute. The minority judgments illustrate arguments that now must be regarded as wrong. McLachlin CJ summarised her position for the majority :
This assumes that the right to a fair trial may not outweigh freedom of religion. And at :
The deleterious effects are the limitation on freedom of religion, the inhibition of complainants and the consequential escape of offenders from justice. Obviously those are hugely important considerations. The salutary effects are preventing harm to the fair trial interest and safeguarding the repute of the administration of justice. The need to find a balance between the deleterious effects and the salutary effects recognises that the salutary effects do not necessarily outweigh the deleterious effects.
It may be that when unfairness goes beyond procedural unfairness and becomes substantive unfairness, it will always outweigh the deleterious effects of requiring a competing right to yield. But that is not clearly stated as the ratio of this case. On its face the majority reasoning has an unpleasant "ends-justify-the-means" blemish.
Although this case is newsworthy for its decision about the wearing of niqabs and the place of religious expression in the courtroom, it has much wider implications. In a contest of competing rights, the majority judgment potentially diminishes the right to a fair hearing in Canada.