[Note: Although there has been mention of a Great Repeal Bill, no such Bill has been published and there is no clear statement regarding the detail of what it may or may not contain. The idea appears to be to freeze the law on the day the UK leaves and then Parliament can make changes in its own time].
The claimants' primary submissions are as follows:
(1) The question in this case is to be approached on the basis that it is a fundamental principle of the UK constitution that the Crown's prerogative powers cannot be used by the executive government to diminish or abrogate rights under the law of the United Kingdom (whether conferred by common law or statute), unless Parliament has given authority to the Crown (expressly in or by necessary implication from the terms of an Act of Parliament) to diminish or abrogate such rights.
(2) No words can be found under which Parliament has given any such authority either expressly or by necessary implication in the ECA 1972 or subsequent legislation relating to the European Union.
(3) The giving of a notice under Article 50(2) of the TEU would pre-empt any ability of Parliament to decide on whether statutory rights should be changed. The notice would automatically abrogate in due course category (iii) rights and the rights under the 2002 Act; it would remove the category (i) rights as enacted by Parliament in the ECA 1972; and it would remove from Parliament decisions on the maintenance of category (ii) rights.
(4) Ratification by Parliament of a withdrawal treaty made pursuant to Article 50(2) (if any such treaty was agreed between the United Kingdom and the European Union) would not cure the pre-emption, as the effect of giving the Article 50(2) notice would in effect inevitably remove the real decision from Parliament.
(5) Parliament had not given authority by the 2015 Referendum Act for the Crown to give notice of withdrawal under Article 50.
The Secretary of State submits as follows:
(1) Parliament could choose to leave (or not to abrogate) prerogative power in the hands of the Crown, even if its use would result in a change to common law and statutory rights,
(2) It was clear from ex p. Rees-Mogg that, unless express words could be found in a statute, Parliament could not be taken to have abrogated the Crown's prerogative powers in relation to the EU Treaties so that notice under Article 50(2) could be given with the consequences that followed in the form of either a withdrawal treaty or automatic departure. Alternatively, applying the guidance in De Keyser's Royal Hotel in the context of the EU Treaties, Parliament could not be taken to have abrogated such prerogative power unless by express words in a statute (or possibly by necessary implication from a statute).
(3) No words could be found in the ECA 1972 or any other statute which abrogated that power expressly or by necessary implication.
(4) In particular, it is notable that neither the 2008 Act nor the EUA 2011 restricted the Crown's prerogative power to give a notice under Article 50(2), even though that provision had come into existence by the time they were enacted. On the contrary, both Acts implicitly recognised that such prerogative power existed as no restriction was placed on the power of the Crown to invoke that right exercisable under the TEU, as amended by the Lisbon Treaty.
(5) Nor were there any express words in any United Kingdom legislation that abrogated the Crown's prerogative power to withdraw from the Treaties as distinct from amending them. That was because the intention of Parliament, in particular as appears from the EUA 2011, was directed at restricting the increase in the powers of the European Union and its encroachment on Parliamentary sovereignty, not at restricting the ability to withdraw from the European Union and thereby restoring Parliamentary sovereignty.
(6) As it is likely that any withdrawal treaty would contain a provision requiring ratification, the withdrawal treaty would in any event have to be approved by Parliament by way of the negative resolution procedure in the CRAG 2010 before that occurred; if it contained provisions requiring application in domestic law, primary legislation would also need to be introduced to allow that. This would be consistent with the proper sequencing of the respective functions of the Crown and of Parliament, as had invariably happened in the past: once an EU treaty had been made, domestic law was brought into line by Parliament through legislation and then the treaty was ratified.
(7) Although the 2015 Referendum Act does not itself confer statutory power on the Secretary of State to give notice under Article 50(2), the implication from the fact that the 2015 Referendum Act is silent on the issue whether legislation is required before notice could be given under that Article supported the contention that Parliament accepted the continued existence of the prerogative powers of the Crown to give such notice; it certainly contains no restriction on such prerogative power as may still exist.