In Ingosstrakh-Investments JSC v BNP Paribas SA [2012] EWCA Civ 644, Stanley Burnton LJ said that “whether the Russian judgment creates an issue estoppel in the present proceedings is a question of English law”. No further explanation was offered, presumably because none was thought to be called for. One may surmise that the unspoken basis for this was that estoppels of this kind, or perhaps of all kinds, are part of the law of evidence and procedure, and effective or ineffective, operative or inoperative, according to the lex fori without any regard to what Russian law might have said on the matter. If that really is so, Professor Garnett would be likely to say that it is not so clear that this is correct. Indeed, in his welcome and timely treatise on the law of substance and procedure in private international law, his general disposition is to find that, where the law is said to be clear, the clarity is either illusory or intellectually inappropriate. The technique which deduces that an issue is to be seen as procedural, and so controlled by whatever rule the lex fori maintains for its disposition, because this is what the cases have said, is regarded as insufficient to persuade the enquiring mind. Garnett would have us all return to first principles. What these are and how they might be refined, is the substance and procedure of this account: the twenty-somethingth volume in a series of Monographs which seems to go from strength to strength.

Private international law, as it has been handed down to us, has always acknowledged a difference between substance and procedure, between issues which may upon proof of foreign law be determined by the application of a foreign law and those which are invariably subjected to the rules of the lex fori despite what foreign law might have said about it. On occasion common law scholarship tries to explain this difference by saying that there is a distinction which takes the form of a line between right and remedy, or between what has to be proved and how it is to be proved.