Thread by @ProfMarkElliott

More than a million signatures notwithstanding, revocation of the UK's Article 50 notification doubtless remains extremely unlikely.

But if revocation were to occur, what would need to happen in legal terms?

A short thread. /1

petition.parliament.uk/petitions/2415…

In this piece, @JolyonMaugham assumes that revocation could be accomplished by the Government using its prerogative powers, without the need for legislation. /2

waitingfortax.com/2019/03/21/we-…

However, it is very hard to see how this could be reconciled with the UK Supreme Court's judgment in the Miller case, in which it was held that Article 50 could not be *triggered* without legislation. /3

publiclawforeveryone.com/2017/01/25/100…

The reasoning in Miller was (in my view) problematic. However, among other things, it reaffirmed the basic constitutional principle that the Government cannot use its prerogative power in a way that would frustrate the intention of Parliament as expressed in legislation. /4

In Miller, I argue that the Supreme Court misapplied this princple, because it wrongly assumed that triggering Article 50 would frustrate the purpose of the European Communities Act 1972. /5

papers.ssrn.com/sol3/papers.cf…

However, whether the prerogative could be used to *revoke* Article 50 would need to be considered against the background of post-referendum leglegislation, including the EU (Withdrawal) Act 2018. /6

publiclawforeveryone.com/2018/06/28/100…

Bearing in mind the approach taken by the Supreme Court in Miller, it would (at the very least) be unsafe to assume that the Government has prerogative power to revoke Article 50. The point is made well by @Prof_Phillipson & Alison Young in this post. /7

ukconstitutionallaw.org/2018/12/10/gav…

It follows that, if Article 50 were to be revoked, it would probably be necessary for legislation to be enacted authorising (or requiring) the Prime Minister to revoke.

(I don't think that the same goes for *extending* Article 50.)

/8

Such legislation could be very short.

It might consist of only one substantive clause.

But it would be necessary in order to remove any doubt about the lawfulness of any notice of revocation served by the UK. /9

Clarity on this point would be important, because in the Wightman case the EU Court of Justice ruled that revocation must be served in accordance with the Member State's constitutional requirements.

That must (among other things) mean that it must be served lawfully. /10

The upshot is that if the UK's notification under Article 50 were to be revoked in a way that would be unequivocally lawful, it would be necessary for Parliament to enact legislation - and to do so very quickly. /ends