Suppose the Government is right about the legal arguments it makes in support of its appeal. Then, unless there is some significant, but completely unforeseen, political development between now and 31 March 2017, a simple letter will be sent giving notification of the UK’s  intention to leave the EU.

The wording will not be elegant. No regret will be expressed.  And two years later, unless other EU states agree to a different outcome, UK citizens will lose their EU citizenship rights.  Parliament may, by then, have passed a Great Repeal Bill that mimics some of those rights in UK law,  but it cannot do so  comprehensively  or perfectly.  The rights that many UK nationals  depend on abroad to work, study, trade,  receive and provide services,  live with family members,  receive healthcare, retire and much besides will be gone in their current form.

In the Divisional Court,  the Government argued that these concerns were exaggerated. Its third QC, Jason Coppel, submitted that the People’s Challenge had:

“seriously overstated the effect of the decision to withdraw from the EU and the notification of that decision on the rights which are conferred on individuals by UK domestic law…. 

The proposition that I want to put to you first of all is that UK citizens have very few rights as EU citizens which are enjoyed as a result of the 1972 Act. Of those rights, none are directly affected by notification and as a matter of law, all could be preserved upon withdrawal, should Parliament so choose.” 

Our view is that this is simply wrong.  That is partly why the EU law specialists in our team, Gerry Facenna QC and David Gregory, produced the Annex to our Written Case cataloging EU citizenship rights and explaining their  fundamental and irreplaceable nature.

That document serves an even more  important purpose, however,  which is to show the Court  just how deep-rooted EU citizenship rights have become,  thanks to the series of Acts of Parliament passed so they could grow in the soil of England,  Scotland, Wales and Northern Ireland and UK territories overseas, like Gibraltar.

The consequences of the Government being right do not stop at a Brexit without Parliamentary control, oversight  or authority, however. To establish the Royal Prerogative can lawfully be used to invoke Article 50 means that the Government has to go much further than arguing it can be used for that purpose. Paragraph 16 of its written case makes this clear:

“… the true  position is that acts of the Government in the exercise of the prerogative can alter domestic law”. 

In other words, the law of the land is only as durable as the executive decides it should be.

The Government  says this is not absolute: Parliament can always protect against the being changed by “expressly or (possibly) by necessary implication” saying this cannot be done in an Act – see paragraph 64. But this  is hardly comforting. Very few Acts of Parliament expressly protect  the rights they create from interference  by the executive,  probably because few Parliamentarian  would have thought that ‘express protection’ was necessary,  given our constitutional arrangements. Protection that is ‘possibly by necessary implication’ is only as good as the legal arguments that can be presented  in favour of it.

Worse still, many of the rights UK citizens enjoy are not contained in statutes at all,  but in the common law. These include the right to procedurally fair decision-making, access to lawyers, protection for confidential legal advice, access to the courts generally  adding specific contexts such as individual liberty, protection from torture, privacy, freedom of religion, freedom of speech and assembly to protest and property rights.

If the Government is right each and every one of these rights only survives as long as it choses not to reach an international agreement to  do away with them.

Laid bare, the Government’s case  is not that it should enjoy prerogative power to  implement the result of the EU Referendum. It is that it should, and does, enjoy prerogative power to change any law unless  prohibited by an Act. That is a remarkable thing for a Government that includes MPs who once argued for cutting back, and strictly regulating, what was left of the Royal Prerogative so that citizens could have more confidence in Parliament’s role.

But maybe this should not be all that surprising. Those with power always want the same thing – more power. That is why Parliamentary democracy,  which balances  the exercise of power with checks and accountability,  however imperfectly,  is something well worth fighting for in the Supreme Court next week.