Parliament gives an official a power, and the official makes a decision you don’t like. So you go to a judge to have the decision reviewed. With any luck, the judge will agree with you and give you a remedy. That’s the normal way of things. But if Parliament is sovereign, then Parliament has the power to prevent the judge from reviewing the official’s decision. All Parliament has to do is include an “ouster clause”: a clause communicating its intention to make the official’s decisions unreviewable.

In the past Parliament has enacted what looks like an ouster clause. It did that most famously in Anisminic Ltd v Foreign Compensation Commission. But judges have tended to say that what looks like an ouster clause is, on closer inspection, not an ouster clause. It seems as if Parliament wants to oust the courts, but really it doesn’t intend that. Now, the clause in Anisminic was a bit ambiguous. It wasn’t as clear as one would wish. So, ever since Anisminic, it’s been a matter of speculation what judges would do when faced with a more clearly drafted clause.

With that as background, the interest in R (Privacy International) v Investigatory Powers Tribunal is understandable (DC | CA). It looks like exactly the sort of test case people were waiting for. There is a putative ouster clause, more clearly drafted than the one in Anisminic. What would judges do? Well, we know the Divisional Court and the Court of Appeal would do – they’ve both said that there is an ouster clause. As a result, they’ve found that certain decisions are immune from judicial review. But it’s likely that the case will be appealed to the Supreme Court, so we’re still waiting for the last word.

I want to show that Bayes’ Theorem provides a helpful way to think of ouster clauses. Bayes’ Theorem is much-discussed in evidence law, but rarely invoked in statutory interpretation. I think it suggests – I don’t put it any more strongly – that Privacy International may have been wrongly decided. Continue reading →