The Judicial College’s Charge Book has this to say about the assessment of witnesses (at 1.6.1.5):
It is generally a misdirection to tell the jury that if they think a witness has an interest in the outcome, they should scrutinise their evidence closely. This is because the jury will likely conclude that the accused has the greatest interest, and so the direction may have the effect of undermining the presumption of innocence (Robinson v R (No 2) (1991) 180 CLR 531; R v McMahon (2004) 8 VR 101).
Practitioners who have learnt from their mistakes will know that this type of submission before a magistrate also has a high potential for ricochet.
Robinson, and in particular the question of generalised directions about witnesses' interests, is presently before the HCA in Hargraves et al v R (a Queensland case.) Heydon in particular questioned its value as a precedent (due to its lack of citations and reasoning!) I wrote an article criticising Robinson (and especially its application to generalised directions) many years ago in the Crim LJ…
(1997) 21 CRIMLJ 273.I will add it to my reading list.
Robinson, and in particular the question of generalised directions about witnesses' interests, is presently before the HCA in Hargraves et al v R (a Queensland case.) Heydon in particular questioned its value as a precedent (due to its lack of citations and reasoning!) I wrote an article criticising Robinson (and especially its application to generalised directions) many years ago in the Crim LJ…
(1997) 21 CRIMLJ 273.I will add it to my reading list.