For example, s 6(6) of the Misuse of Drugs Act 1975[NZ] applies when a person has been proved to have been in possession of a specified quantity of a drug, and it operates by creating a presumption that the person had the purpose of supplying it, "until the contrary is proved". This has been held to mean that the defendant has the legal burden – that is, to the standard of the balance of probabilities – of proving absence of that purpose: Hansen v R  NZSC 74. The Supreme Court held that "proved" means proved on the balance of probabilities, and it rejected an interpretation of "proved" which was that it means the burden of raising a reasonable doubt, that is, the evidential burden. For my earlier commentary, see 13 January 2010, 5 March 2009, 20 February 2007, and 19 September 2005.
This latter, rejected, interpretation of "proved" was based on a suggestion by Glanville Williams in "The Logic of 'Exceptions'"  CLJ 261, 265. I had relied on that article in making submissions (also rejected) to the New Zealand Court of Appeal in R v Phillips  3 NZLR 175. In that case, Cooke P for the Court found that interpretation of "proved" a "strained and unnatural interpretation".
The House of Lords did not find it "strained and unnatural" in R v Lambert  UKHL 37, and indeed at  Lord Steyn said:
Much can turn on the interpretive directions given by the constitutional legislation.
The same submissions about the reverse onus were made in Momcilovic v R  HCA 34 (8 September 2011). The wording of the reverse onus provision here was different and was held to be unambiguous, in that it requires the defendant to "satisfy the court" of the specified matter. "Satisfy" has always been understood to mean to establish on the balance of probabilities. See French CJ at 62, Crennan and Kiefel JJ jointly at 581 and Bell J at 659. That applied to proof of possession of the drug. But as to possession for the purpose of trafficking, the legislation did not impose a presumption and so the possession and the purpose had to be proved by the prosecution to the standard of beyond reasonable doubt: French CJ at 72, Gummow J at 200 (Hayne J agreeing at 280), Crennan and Kiefel JJ at 611 and Bell J at 659.
Momcilovic is, in addition, full of dicta of interest to those who are concerned with the Australian constitutional legislation.