The question of whether the deal that broke the deadlock in Brexit talks is legally binding has been the subject of much discussion since the agreement was announced on December 8. Technically, the answer depends on whether you look at the question from the point of view of law or politics. But more broadly, this is a classic example of a case where law and politics are closely linked.

The withdrawal agreement to set out the terms of Brexit will be an international treaty between the UK and the EU, according to the wording of Article 50 of the Treaty on European Union, which refers to an “agreement”. Treaties are legally binding, according to the Vienna Convention on the Law of Treaties.

So is the agreement published on December 8 a treaty? It takes the form of a “joint report” of the negotiating parties – the UK and the remaining 27 members of the EU (EU27) – and does not have the usual elements of an international treaty, such as a date of entry into force or signatures of the parties. However, from a legal point of view, there are no formal requirements to meet before defining something as a “treaty”. Instead, the Vienna Convention states that the crucial issue is the “consent to be bound” by a treaty.

The fine print

Applying this test, it’s obvious there is no “consent to be bound” by the recent deal. So it is not a treaty – and therefore not legally binding.

The first paragraph states that it “records the progress made in the first phase of negotiations”. There was agreement in principle on some issues such as EU citizens’ rights, and progress on agreeing on some others, including the Irish border. The negotiations are not complete, but have come a significant way.

The crucial points – from both a legal and political perspective – are set out in the fifth paragraph of the text:

Under the caveat that nothing is agreed until everything is agreed, the joint commitments set out below in this joint report shall be reflected in the Withdrawal Agreement in full detail. This does not prejudge any adaptations that might be appropriate in case transitional agreements were to be agreed in the second phase of the negotiations, and is without prejudice to discussions on the framework of the future relationship.

Taken together, it is clear that the joint report is a summary of the negotiations toward the legally binding withdrawal agreement, rather than any sort of legally binding text of its own. But, this brings us to the question of whether the text is in some sense “politically” binding.

The political perspective

The purpose of having a review of negotiations at this point is for the EU27 to judge whether there has been “sufficient progress” on three key issues – the financial details of Brexit, the legal status of UK and EU27 citizens who have moved, and the Irish border – to move to a second phase of talks. This means talks about the future trade relationship between the UK and the EU after Brexit can begin.

Since the Joint Report is not itself a treaty, there will be no legally binding obligations until and unless that second phase of talks is concluded successfully. Put another way, the report is not a “default” that will somehow be transformed into a legally binding text if the next phase of talks fails. That’s what the phrase “nothing is agreed until everything is agreed” means.

Olivier Hoslet/EPA

However, the Joint Report refers to “joint commitments” which “shall be reflected in the Withdrawal Agreement in full detail”. A “commitment” is a promise – and even when a promise is not legally enforceable, breaking it usually has consequences. In this case, if the UK is unwilling to stick to the commitments it made in the Joint Report, the EU27 side will likely refuse to discuss the future trade relationship, and it is likely there will be no full Brexit deal.

Some Leave supporters may believe that the EU27 is bluffing on this, or that it would at least agree to sign a series of smaller deals – what I like to call the “deal and no deal” scenario. But Brexit supporters’ predictions of what the EU27 would do have been wrong before: German carmakers have not forced the whole EU27 to cave in to everything the UK wanted within a matter of days, as some suggested. The side that “holds all the cards” in negotiations does not usually end up agreeing to pay the “weaker” side tens of billions of pounds.

So while it is technically accurate to say the new deal is not legally binding, that would be misleading regarding its political importance. The UK can quite reasonably argue about the finer details of what it signed up to in the next stage of negotiations. But suggesting that the agreement has no significance whatsoever frankly signals a lack of good faith.