So even before the Ponsonby rule came into effect in 1924, there was this constitutional requirement, we submit, for Parliament's consent to be given to ratification of the accession treaty. Now, neither the Ponsonby rule nor CRAG apply to treaties which are required to be implemented under domestic law. Contrary to my learned friend Mr Eadie's submissions, CRAG and the subsequent legislation is nothing to the point on the question of withdrawal from a treaty under Article 50. There is this prior fundamental lock, we would submit, and that lock is brought about by the fact that the EU treaties require implementation in domestic law.
Now, the reason I go through all that history at quite some length is for two reasons. First, it demonstrates, we submit, the interaction of the doctrine of parliamentary sovereignty and the UK's dualist approach to international treaties. The treaties could have no impact on domestic law without the 1972 Act, but it was an absolutely essential feature of the treaties, as international law instruments, that much of them should have and should be given effect in domestic law.
So the 1972 Act was essential. If the treaties could not have had effect in domestic law, without Parliament passing the 1972 Act, so it must be that the effects of those treaties in domestic law can only be removed by Parliament and not by the executive. The key point about the dualist system from a parliamentary sovereignty perspective is that, when the UK enters into a treaty which requires domestic implementation, Parliament remains in control of the process. It remains in control if the necessary enabling legislation is passed or not. Parliament has a free choice. If Parliament refuses to pass the legislation, the treaty is not ratified.
Now the corollary of Parliament having that control is that parliamentary control must equally apply to the withdrawal process. It is for Parliament to choose whether it will repeal the legislation which implemented the treaty in domestic law.
For that reason, Parliament remains in effective control, whether the UK withdraws from the treaty or not.
The difficulty with the appellant's argument is that the triggering of Article 50 by the Government alone will bypass that parliamentary control, and it will rob Parliament of any substantive choice as to whether or not to repeal the 1972 Act.