Roughly half of the country is reeling this morning from the  news that the people of United Kingdom have voted — by a narrow but clear majority — to leave the European Union. There is a great deal to be said about what might happen next, and I expect to post regularly as events unfold about the legal and constitutional aspects of the Brexit saga. (And it will be a saga.) But, for now, I will confine myself to five brief thoughts.

First, the markets may be in freefall, but the UK remains a member of the EU this morning. It is therefore still bound by the European Union treaties, and the European Communities Act 1972 remains in force. This means that, as a matter of international law, the UK as a State continues to be subject to its obligations under the EU treaties, and that, under the 1972 Act, EU law remains applicable in the UK and has priority over UK law. Legally and constitutionally, nothing has changed yet. Freedom of movement remains a legal right of UK citizens as citizens of the EU. (Enjoy it while it lasts.) Nothing will change until either the UK extracts itself from its obligations under the EU treaties or declines to discharge those obligations by amending or repealing the European Communities Act.

Second, as far as the position in international law is concerned, there are two ways in which the UK could extract itself from its obligations under the EU treaties. One possibility is treaty amendment under Article 48 of the Treaty on European Union. However, as my colleague Professor Kenneth Armstrong has pointed out, this would require unanimous agreement among Member States and would involve circumvention of the specific mechanism, contained in Article 50, for departure from the EU. Article 50, therefore, is by far the more likely vehicle for Brexit. Under it: “Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.” Once the Member State makes the decision to withdraw and gives the European Council notice of its intention to leave, the clock begins running and — subject to two exceptions — the treaties cease to apply to the departing Member State after two years. The first exception is that the two-year rule does not apply if the departing State reaches agreement on the terms of departure before the expiry of the two-year period. The second exception is that the European Council — with the agreement of the departing State — can agree to extend the negotiation period beyond two years.

Third, the likelihood, therefore, is that Brexit will be accomplished under Article 50. That means that — unless matters are wrapped up earlier by mutual agreement  — the UK will remain a Member State of the EU for at least two years from the date on which notice of the UK’s intention to leave is served upon the European Council. And that gives rise to the question whether — and, if so, when — notice must be served. As a matter of law, notice does not have to be served — ever — because the outcome of the referendum is not legally binding. The legislation that provided for a referendum to be held said nothing whatever about the effect of the outcome of the referendum, and the result does not place the Government under any legal obligation to secure Brexit — whether by serving notice on the European Council under Article 50 or otherwise. Put another way, the United Kingdom has not, simply by holding an advisory referendum, “decide[d] to withdraw” within the meaning of Article 50. Rather, the will of the people has been expressed through an advisory referendum, and the making of the decision whether to withdraw remains a matter for the Government.

However, to say that the Government is not legally obliged to trigger Brexit is one thing. Political reality is something else entirely. It would, self-evidently, be astonishingly political difficult for the Government to ignore the outcome of the referendum, and there is, in effect, an insuperable political obligation to fire the Article 50 starting-gun. That does not, however, mean that the UK Government must — or should — immediately do so. Given that it is not obliged by UK law or by EU law to start the Article 50 process, it can, if it wishes, bide its time — in order, if nothing else, to take stock and work out who, and by reference to what strategy, the negotiations will be conducted. The UK could, for instance, decline to trigger the Article 50 process until a new Prime Minister takes office in the autumn — which is what David Cameron appeared to envisage would happen in his resignation statement.

Fourth, the question arises whether the UK Government — whether in its present or some revised configuration — might be so impatient about Brexit as to seek to hasten its practical consequences by amending or repealing the European Communities Act 1972. The Act might, for instance, be amended so as unilaterally to qualify or remove the principle that EU law takes priority over UK law, to block new EU laws from taking effect in the UK, or to adjust or displace the jurisdiction of the Court of Justice of the European Union in respect of the UK. Such steps would, however, be highly inadvisable, not least because they would risk legal chaos by placing the British and EU legal regimes on a collision course with one another prior to the UK’s having extricated itself, as a matter of international law, from the EU legal order. It is in no-one’s interests — including Britain’s — that the UK should play fast and loose with its international obligations; at a time of immeasurable instability, an orderly departure is imperative.

That is not to say that the European Communities Act will not, at some point, need to be repealed: it certainly will have to go. But two things will have to happen before the Act is excised from the statute book. First, the UK must square the international and domestic legal positions by ensuring  that its international obligations to give effect to EU law are extinguished before the domestic legal apparatus for giving effect to those obligations is dismantled. And, second, the dismantling of that apparatus — which will be no mean feat — must itself take place in an orderly manner. Indeed, it is no exaggeration to say that the process of disentangling EU and domestic law will be a Herculean effort that will occupy law-makers for a considerable amount of time to come, and will have to be undertaken carefully and thoughtfully.

Fifth, finally, and most significantly, the question arises whether Brexit represents an existential threat to the United Kingdom itself. The answer must be that, at the very least, it poses a risk. Earlier this morning, the First Minister of Scotland — referring to the pro-EU posture adopted by Scottish voters in the referendum — said that “the vote makes clear that the people of Scotland see their future as part of the European Union”. If that is so, then the implication is that the people of Scotland do not see themselves as part of a United Kingdom that has taken what appears to be an irrevocable decision to remove itself from the EU. It need hardly be pointed out, therefore, that the likelihood of a second Scottish independence referendum must be markedly greater today than it was 24 hours ago.

The brutal truth is that if the Scottish people — or the people of Northern Ireland — wish to be part of the EU, then they must leave the UK. Their hands will now therefore be forced, since however flexible the British constitution might be, the harsh reality is that the UK, and only the UK, is a State in international law — meaning that its constituent nations cannot be Member States of the EU unless they first acquire statehood themselves by exiting the UK. These are very early days, and events will move quickly and unpredictably. The break up of the United Kingdom, just like the UK’s formal departure from the EU, will not happen today or tomorrow. But just as the latter is now a certainty, the former must now be a distinct possibility, if not a probability. For that reason, if no other, the legal and constitutional implications of the Brexit vote cannot easily be exaggerated.