BA v The Queen  VSCA 285 represents as clear a judicial conclusion as you are likely to find. While dismissing the appeal, Buchanan JA [at 21, Maxwell P and Osborn JA agreed] said briefly:
The fourth ground of appeal is that the trial judge erred in holding that a witness could not give evidence as to the general reputation for veracity of the complainant.
At common law evidence is admissible to impeach the veracity of a witness. The rule is stated by Archbold in these terms:
In order to impeach the credit of a witness for veracity, witnesses may be called by the other side to prove that his general reputation is such that they would not believe him upon his oath: Archbold, Criminal Pleading Evidence and Practice 2009, [8-153]. See R v BDX  VSCA 28.
Counsel for the appellant, relying upon these authorities, sought to lead evidence from the complainant’s mother as to whether she believed the complainant’s allegations against the appellant, that the complainant frequently lied and that she would not believe the complainant on her oath.
The trial judge ruled that Part 3.7 of the Evidence Act 2009 [sic] (‘the Act’) ousted the common law rule and the evidence was not admissible.
Section 102 of the Act provides that credibility evidence about a witness is not admissible. Section 101A defines credibility evidence as evidence that is relevant only because it affects the credibility of a witness or is relevant because it affects the assessment of the credibility of a witness and for some other purpose for which it cannot be used because of a provision in the Act relating to hearsay or opinion. That provision, which the Act describes as ‘the credibility rule’, is succeeded by three sections containing detailed exceptions to the rule. It was not disputed that none of the exceptions applied in the present case.
In my opinion, it is apparent that Part 3.7 of the Act covers the field by establishing a general rule subject to a number of limited exceptions. To revert to the common law would effectively abrogate the statutory rule.
(Those statutory exceptions are mostly found in ss 103 and 106. They didn't apply in this case.)
BA makes it unlikely that trials of the sort considered in R v BDX  VSCA 28 will make a resurgence. It makes sense not to retain the common law in this area - just as, if common law rules still applied to identification evidence, the more restrictive requirements on the prosecution found in Part 3.9 would be made redundant.
Going by the description of the facts provided in the judgment, this was not a case where the complainant's mother - at the time of the alleged offences, the appellant's partner - had any direct knowledge of the incidents in question, or where her evidence on a substantial issue might have contradicted the evidence of the complainant, as in Best v The Queen  VSCA 277. Asking the relative of the complainant in an incest case whether they believe the allegations seems unhelpful, at best (even if it escapes the threshold test at s 55 because of s 55(2)(a)).