The idea that Parliament can prevent the UK from crashing out of the European Union without any withdrawal agreement appears to be taking hold. But can Parliament really stop a cliff-edge, ‘no deal’ Brexit? And — a related question — can it veto Brexit if a deal is agreed that parliamentarians consider to be an unacceptable one? Some MPs’ recent contributions to public debate imply that Parliament ultimately remains in the driving seat because it is sovereign, and can therefore enact whatever legislation it wants, including legislation putting the brakes on Brexit in a ‘no deal’ or a ‘bad deal’ scenario.

This is true — but only in an irrelevant sense. Parliament can say whatever it wants in a Bill. The European Union (Withdrawal) Bill could thus, for instance, be amended to provide that MPs must be given an opportunity to vote on any deal agreed between the UK and EU governments. It could even stipulate that the UK is not to exit the EU unless there is a deal that MPs consider acceptable. But such statutory provisions would amount to nothing more than the legislative equivalent of the instructions issued by King Canute to the incoming tide. For just as Canute could not control the laws of nature, so the UK Parliament’s sovereign capacity to make domestic law cannot be used to control the operation of EU law. The EU law in question is Article 50(3) of the Treaty on European Union. It provides that:

The [EU] Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.

The effect of Article 50(3) is that, by default, EU law will operate so as to eject the UK from the EU on 29 March 2019: two years after the UK Government, under Article 50(2), notified the EU of the UK’s intention to withdraw. This, then, is the essential legal fact that shapes the options that are — and, crucially, are not — open to the UK Parliament.

The most important point to note is that there is nothing that the UK Parliament can do, by enacting legislation, that alters the legal effect of Article 50(3). Unless the two-year Brexit clock — which is counting down inexorably to exit day in March 2019 — is stopped, or the two-year period extended, the UK will leave the EU. It might do so with a transitional agreement in place, or with no such agreement in place. It might so (albeit this is unlikely) with a full withdrawal agreement in place, or with no such agreement in place. And it might do so with a good deal, a bad deal, or no deal. But the default position is that it will leave: it will cease to be a party to the EU Treaties, and it will no longer be a Member State. And no amount of domestic legislation can unilaterally alter that simple legal fact, precisely because it is a legal fact that derives from EU law that Parliament, as a domestic legislative institution, cannot itself change.

Is that it, then? Or is there something — anything — that Parliament can do? It might legislate to the effect that unless it is happy with the deal, the UK Government is legally obliged to cancel Brexit by unilaterally withdrawing the notification that triggered the Article 50 process in the first place. But that presupposes that the UK’s Article 50 notification can be unilaterally revoked: a question that is shrouded in legal uncertainty, given that Article 50 is itself silent on the point, and given that it is an issue that has never been litigated. It follows that Parliament could, in this way, attempt to block a ‘no deal’ or a ‘bad deal’ Brexit by blocking Brexit itself, through the cancellation of the Article 50 withdrawal process; but there is no guarantee that it would succeed, given that Article 50 might not be unilaterally revocable.

A second possibility is that Parliament might stipulate — in the EU (Withdrawal) Bill or elsewhere — that in the absence of a deal considered satisfactory by parliamentarians, the UK Government is required to negotiate with the EU27 in order either to get their agreement that the UK’s Article 50(2) notification be put to one side or that the two-year negotiation period be extended. But this, too, offers no guarantee. Article 50(3) is very clear that the two-year period cannot be extended save by a unanimous decision to that effect, meaning that any one of the EU27 could veto such a step.

A third possibility has been identified by the so-called ‘Three Knights Opinion’, written by Sir David Edward KCMG PC QC, Sir Francis Jacobs KCMG PC QC, Sir Jeremy Lever KCMG QC, Helen Mountfield QC and Gerry Facenna QC. They argue that:

[T]he United Kingdom is entitled to say to the European Union: ‘We have decided to withdraw and here is our notice under Article 50. However, since withdrawal will involve a fundamental change to our laws and will inevitably amend or abrogate individual rights, the terms of withdrawal, in so far as they have such a consequence, can be given effect under our constitution only by an Act of Parliament, and our decision to withdraw is therefore subject to approval of the terms of withdrawal by our Parliament.’

They go on to argue that the European Union (Notification of Withdrawal) Act 2017 authorised only the notification of withdrawal, and did not authorise the removal of any particular domestic law rights. Moreover, they contend that ‘parliamentary sovereignty and the principle of legality require Parliament expressly to authorise withdrawal from the European Union on the terms agreed with the European Union, or to authorise withdrawal if no acceptable terms can be agreed’, and that nothing less than primary legislation can supply such authorisation. On this analysis, the domestic legal changes inherent in Brexit could not legally and constitutionally have been authorised in advance by the 2017 Act, and can be authorised only by legislation enacted by Parliament once it knows what the terms of Brexit actually are. Crucially, the ‘Three Knights’ argue that the need for parliamentary authorisation at the end of the process dovetails with Article 50 itself, because such authorisation is one of the UK’s ‘constitutional requirements’. On this view, Article 50(3) would not operate to eject the UK from the EU if one of those requirements — i.e. parliamentary endorsement of the withdrawal terms — were unforthcoming.

This analysis, however, is unpersuasive, not least because it flies in the face of the majority’s reasoning in R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5. Indeed, the whole Miller case was premised on the notion triggering Article 50 would involve the initiation of a process that would fundamentally change UK law and strip those to whom it applies of myriad legal rights. It was for precisely that reason that the Supreme Court held that only Parliament could pull the trigger firing the Article 50 bullet. But if the ‘Three Knights’ are right, and Brexit cannot happen without legislation enacted at the end of the negotiation process, then any objection to Article 50 being triggered using the prerogative is swept away, because the initiation of the Article 50 process could never in itself result in Brexit. The incompatibility of the ‘Three Knights’ argument with Miller suggests that very little, if any, store should be set by that argument.

So can Parliament block a ‘no deal’ or a ‘bad deal’ Brexit? The answer must be that it cannot do so unilaterally unless the UK’s Article 50(2) notification is unilaterally revocable, in which case Parliament could insist that the UK Government withdraws that notification if Parliament decides that no acceptable deal has been reached. But, as noted above, it is far from clear that the UK’s notification can be unilaterally revoked. The United Kingdom Parliament may be sovereign when it comes to UK law. But it has set in train a process that is now unfolding in EU law and which (if Article 50 is not unilaterally revocable) it cannot itself determine. Therein lies one of the (many) delicious ironies of Brexit. The ultimate objective might be ‘taking back control’ (whatever that means), but it involves a process from which control — at least from the perspective of UK parliamentarians — is notable by its absence.