Where a judge has to balance one consideration against another, is the determination of the weight to be given to each consideration a question of fact or of law?
Yesterday the United Kingdom Supreme Court held that weight is a question of fact: Secretary of State for the Home Department v AP  UKSC 24 (16 June 2010), at para 12:
"The weight to be given to a relevant consideration is, of course, always a question of fact and entirely a matter for the decision-maker – subject only to a challenge for irrationality which neither has nor could have been advanced here. All this is trite law and indeed the contrary was not argued before us."
The context here was whether the conditions of a control order made under the Prevention of Terrorism Act 2005[UK] breached article 5 of the European Convention on Human Rights, the right to liberty. The Court held that restrictions on liberty that might otherwise have been justified might be rendered unjustifiable when a breach of the right to respect for private and family life (article 8) is taken into account. Because article 8 is relevant it is capable of tipping the balance.
That sort of balancing has wider application than just control orders. Bail conditions must be reasonable. Evidence improperly obtained may or may not be admissible, depending on a balancing of public and private interests. Are these balancing exercises always questions of fact unless they are done irrationally?
The question is significant where there are limitations on rights of appeal to questions of law.
As I noted earlier (18 May 2010) in R v Gwaze  NZSC 52 the New Zealand Supreme Court held that decisions on the admissibility of evidence are decisions on questions of law. Such decisions can involve balancing of competing rights, particularly under s 30 Evidence Act 2006. If these were questions of law, the weight given to relevant considerations would not be entirely for the decision-maker. What seemed "trite" to the UKSC in the context it was addressing in AP is certainly not trite in the Gwaze context.