Negotiating Brexit in the Shadow of the Law of Treaties

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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.


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Daniel Peat says

March 12, 2019

Dear Marko,

What a fascinating day -- never before have I seen so many MPs trying to grapple with the niceties of the law of treaties.

On your first point, the AG was particularly vague in responses to MPs' questions in the Commons today. At some points, he asserted that the Joint Declaration created new legal obligations (i.e. that it constituted a new treaty), whilst his written advice seems to limit the Declaration to Art. 31(2)(b) VCLT. Obviously, he was obliged to argue the former for political reasons, unconvincing as that might be.

Also in relation to your first point, I note that the 'authentic interpretation' language that he used reflects the ILC's understanding of the elements of interpretation under Article 31 when they were originally drafted. When explaining the structure of what would become Articles 31 and 32, Waldock stated that "the distinction made in articles 27 and 28 [now articles 31 and 32 VCLT] between authentic and supplementary means of interpretation is both justified and desirable" (Draft Articles on the Law of Treaties with commentaries, (1966) II YBILC 220, para. 10). So I don't agree with you that an 'authentic interpretation' is stronger than an agreement in the sense of Art. 31(2)(a) VCLT: the ILC considered the latter to be a species of the former.

Finally, in relation to your fourth point, the AG seems to place inordinate belief in the ability of the UK to demonstrate the EU's bad faith. Only a cursory glance at ICTs' jurisprudence shows that it is exceptionally hard to prove a state acted in bad faith. In the Tacna-Arica Arbitration, for example, the arbitrator considered that bad faith amounted to "something more...than the failure of particular negotiations" that must be supported by "clear and convincing evidence which compels such a conclusion" ((1925) II RIAA 930). I think that the UK would be wildly misguided to place much weight on its ability to prove bad faith.