Even the most robust of the fundamentals of the criminal law can be modified by statute. When that happens, the fundamental should retain its strength in all cases to which the statutory modification does not apply.
But sometimes a statute is not explicit on whether it modifies a fundamental of the criminal law, while its purpose seems to require such a modification. If a court accepts that this sort of statute does indeed modify a fundamental of the criminal law, there is a danger that it will support its conclusion by pointing to weaknesses in the fundamental. Those weaknesses may later be used in support of interpretations of other statutes to override the now weakened fundamental.
To bring these considerations into focus, consider Lee v New South Wales Crime Commission  HCA 39 (9 October 2013). The relevant fundamental of the criminal law was the principle that the prosecution must discharge the onus of proof and cannot compel the defendant to give evidence to help discharge that onus:  per Kiefel J dissenting.
Lee concerns the civil procedure, under the Criminal Assets Recovery Act 1990 (NSW) (the "CAR Act") of compulsory examination of a person to establish whether assets were probably obtained through serious crime. The examinee was also subject to criminal proceedings, and this gave rise to the issue whether the examination should be delayed until the trial had been concluded, so as not to give the prosecution an unfair advantage.
This sort of issue has arisen before: X7 v Australian Crime Commission  HCA 29 (26 June 2013), discussed here on 27 June 2013. In that case the conclusion reached by the majority (Hayne, Bell and Kiefel JJ) was the opposite of that reached by the majority in Lee (French CJ, Crennan, Gageler and Keane JJ). The new players are Gageler and Keane JJ, who delivered a joint judgment in Lee).
A focus on the judgment of Gageler and Keane JJ should therefore reveal the points that carried the day in Lee. The appellants' argument, as refocused in oral submissions, is summarised at -. The inherent prejudice in allowing an examination while criminal charges are pending is, according to this analysis :
" ... the answers given and documents produced by the person in the examination would inevitably constrain the instructions on which the legal representatives of the person could act in the criminal proceedings: the legal representatives would be ethically bound not to lead evidence or cross-examine or make submissions to suggest a version of the facts which contradicted that given by their client on oath in the examination."
The assumption here is that the legal advisers know what the examinee had said during the examination. Normally, a client does not give instructions on oath, and a client's prior statements are not given on oath. A difficulty would only arise if answers given on oath at examination became admissible against the examinee as defendant at trial. So the constraint on instructions referred to at  can be avoided if answers at examination are not disclosed to the legal representative in the criminal proceedings, and if those answers are not admissible to rebut the defendant's defence at trial.
However instead of adopting this sort of harm-containment approach, Gageler and Keane JJ took a swipe at the principle of construction (that the legislature does not intend to alter the law beyond the immediate scope and object of a statute ) that fundamental rights are not altered by a statute unless that is expressly done. They adopted Gleeson CJ's view that in modern times the strength of that principle will vary with context . But it is not necessary to qualify the strength of this principle of construction, to make the point that the clear intention of a statute may be to alter fundamental rights.
In addition to weakening the principle of construction, Gageler and Keane JJ weakened the fundamental principle of the criminal law that a defendant cannot be compelled by process of law to admit the offence, by saying it is "not monolithic: it is neither singular nor immutable" . Some statutory inroads on the right to silence do not mean that the right is weakened where it does apply. It was unnecessary for the judges to suggest this weakening.
The more conventional part of this judgment addresses directly the interpretation of the CAR Act - and reaches the, no doubt sound, conclusion that :
"The power conferred by s 31D(1)(a) does not authorise the making or implementation of an examination order where to do so would give rise to a real risk of interference with the administration of justice including by interfering with the right of the person to be examined (or any other person) to a fair trial. For reasons already given, however, the making of such an order does not give rise to a real risk of interference with the administration of justice by reason only that the subject-matter of the examination will overlap with the subject-matter of criminal proceedings that have commenced but that have not been completed."
And importantly, as to the way the discretion to order an examination should be exercised, :
"The reasons for judgment of the Court of Appeal do not suggest that the CAR Act indicates a legislative intention that the Supreme Court should allow any proceedings under that Act to proceed if the circumstances of the case, other than the mere pendency of criminal proceedings against the examinee, were such as to reveal a real, as opposed to a speculative or theoretical, risk that the administration of justice would be adversely affected. The exigencies of criminal proceedings might well afford a ground for a refusal to make an order under s 31D(1)(a). For example, the timing of an application may be such as to prejudice the fair trial of a criminal charge because of the likely disruption of the preparation for, or conduct of, a trial which is imminent. As Beazley JA specifically noted , that possibility was not raised before the Court of Appeal as a consideration having a claim upon the discretion in the circumstances of this case. Had it been raised, it would obviously be a consideration which might properly be taken into account in exercising the discretion."
This conclusion could have been reached without suggesting that the rule of construction or the right to silence are in any general sense weakened these days. Lee required merely a conventional exercise in statutory interpretation.
A similar position exists under comparable New Zealand legislation: Criminal Proceeds (Recovery) Act 2009, s 107. In each case a careful analysis has to be made of the matters which the Commissioner wishes to examine the defendant about, and the likely impact of answering those matters on the subsequent criminal trial: Commissioner of Police v Wei  NZCA 279 at .