Don't mention the elephant

Back in 1991, the High Court stated that:

in examining the evidence of a witness in a criminal trial – including the evidence of the accused – the jury is entitled to consider whether some particular interest or purpose of the witness will be served or promoted in giving evidence in the proceedings. But to direct a jury that they should evaluate evidence on the basis of the interest of witnesses in the outcome of the case is to strike at the notion of a fair trial for an accused person.

These two sentences seem to set down a proposition that while the jury are entitled to consider whether some interest of the accused would be served by giving the evidence he has (such as, you know, securing an acquittal), it is an error of law for the judge to tell the jury that. Yesterday, the High Court reiterated that prohibition.