Negotiating Brexit in the Shadow of the Law of Treaties

It is an extraordinary day in British politics today, with the Prime Minister’s ‘enhanced’ Brexit deal to be voted on in Parliament later this evening. The outcome of today’s vote, and the votes that may follow later in the week, is of course anyone’s guess (although the WA will likely be voted down). I have now read through the Attorney-General’s new legal advice on the revised deal and have been following the debate in the House of Commons, and was struck by how remarkably the various issues being debated turned around the customary law of treaties, which operates by default, in the background, unless the UK and EU agree differently. Here are just some – readers are of course invited to discuss any relevant matter in the comments:

(1) What is the legal nature of the Joint Instrument relating to the Withdrawal Agreement, and what are its legal effects? Is it an agreement in the sense of Art. 31(2)(a) VCLT, which defines the ‘context’ of the treaty? Is it something even stronger, an ‘authentic interpretation’ of the WA? Is is also a separate treaty, even though it is not called such, because it is a written agreement between a state and an IO governed by international law, which sets out further obligations that were not in the WA? (The latter is the position of the UK government).

(2) Note in that regard the superb example of constructive ambiguity of the final paragraph of the Instrument, which allows the EU to say, on one hand, that the WA was not reopened or changed as the Instrument simply interprets the WA, and for the UK to argue that meaningful legally binding changes were made to the deal:

Note that this instrument provides, in the sense of Article 31 of the Vienna Convention on the Law of Treaties, a clear and unambiguous statement by both parties to the Withdrawal Agreement of what they agreed in a number of provisions of the Withdrawal Agreement, including the Protocol on Ireland/Northern Ireland. Therefore, it constitutes a document of reference that will have to be made use of if any issue arises in the implementation of the Withdrawal Agreement. To this effect, it has legal force and a binding character.

(3) Similarly, what is the legal nature and effects of the UK’s Unilateral Declaration? Is it simply an interpretative declaration by the UK, which is of itself incapable of having any direct legal effects, being simply a statement of the UK’s position? Or is it something more, especially because the EU has not objected to it?

(4) There seems to be consensus that the customary rules on denunciation and suspension of treaty obligations have been displaced by the express dedicated provisions of the WA. This seems to apply also for termination or suspension due to material breach. The WA does not allow the UK to exit the backstop unilaterally; it can only suspend obligations arising from it if the EU is shown to be acting in bad faith and this is determined by the arbitral tribunal established by the WA.

(5) However, the UK’s position is that it CAN unilaterally terminate the WA or the backstop Protocol in case of fundamental change of circumstance/rebus sic stantibus. The Attorney General was explicit on the point repeatedly in the Commons. Never has more been at stake, it seems, regarding the interpretation of the rule in Art. 62 VCLT.

We’ll obviously have to wait and see how this will play out, but again it is clear that Brexit is being shaped critically by the background operation of the law of treaties. It is also remarkable how much importance has been given to questions of form, i.e. how crucial it is for many MPs whether a particular obligation is political or legally binding. Readers may also be interested in the Attorney’s new advice; the Attorney’s prior advice on the WA; an opinion by David Anderson QC, Jason Coppel QC, and Sean Aughey; and an opinion by Philippe Sands QC and David Edward QC.