Lord Grabiner focused on the illegality defence. The scope of this defence is now so uncertain that the Supreme Court has suggested that it needs the urgent attention of a seven or nine member panel of that court (Bilta v Nazir, 2015). The principal tension is one between certainty and flexibility. The advantages of a rule that is certain are obvious: it pays attention to the needs of litigating parties and their advisers, and the idea of the rule of law. Yet the complaint can be that outcomes can seem to rest on a technicalities.