The Impact of Brexit on Global Treaty Relations

Dr. Joris Larik, Assistant Professor of Comparative, EU and International Law at Leiden University, discusses the impact of Brexit on global treaty relations and sheds light on the emerging practice to date, showing that Brexit has spawned the creation of numerous new international legal materials.


This article draws on an article Dr. Larik recently published in the American Journal of International Law.


On 1 February 2020, the Agreement on the Withdrawal of the United Kingdom of Great Britain and Northern Ireland from the European Union and the European Atomic Energy Community (commonly known as the “Withdrawal Agreement”) entered into force. This concluded three-and-a-half years of difficult negotiations following the June 2016 referendum and put an end to the UK’s forty-seven years of EU membership.

On the one hand, there have been many examples throughout history of countries disintegrating or parts of them breaking away. Think of the violent breakup of Yugoslavia or the independence of South Sudan in 2011. On the other hand, in the realm of international organisations, there are instances of members withdrawing and organisations disbanding. Take the dissolution of the League of Nations’ in 1933 and more recently the withdrawal of the Philippines from the International Criminal Court as examples.

Brexit, however, falls in-between these two categories. It concerns leaving an entity that is more than a traditional international organisation. Rather, one could consider it “a supranational institution that in some ways resembles a nation” – though in other key aspects it certainly does not. Withdrawing from the EU, crucially, is far from a purely intra-European issue. Brexit raises questions about the applicability of hundreds of international agreements to the UK, for which there are no ready-made answers in international treaty law and of which legal scholarship has only started to make sense.

A global recalibration of treaty relations

The UK’s future as a global treaty-maker is a highly charged political topic. The vision of “Global Britain” boldly setting out to strike trade deals around the world has long been a prominent argument of the Brexiteers. We can recall Boris Johnson’s first speech as Prime Minister, which included a call to “start now on those free trade deals” and “to recover [the UK’s] natural and historic role as an enterprising, outward-looking and truly global Britain”.

Due to the Withdrawal Agreement and its transition period, the UK is going through a gradual increase in its external treaty-making powers that correspond to a phased decrease of the constraints that EU (external relations) law imposes on it. The practice to date provides the outlines of how the UK, the EU, and treaty partners around the globe respond to the novel questions raised for the law of treaties prompted by a country’s withdrawal from a deeply integrated supranational entity that is also an avid treaty-maker.

In a nutshell, the practice can be summarised in three phases:

  • Prior to withdrawal, the UK had already been conducting (preliminary) trade negotiations with a range of external partners, in some cases already signing so-called “continuity agreements” which largely reproduce the contents of agreements concluded by the EU. It was doing so while still being a member state, which may have been in breach of exclusive EU competences and the duty of sincere cooperation (as laid down in Article 4(3) of the Treaty on European Union). Launching these negotiations suggests that governments – including the UK – did not consider that the rights and obligations under international agreements concluded by the EU with external partners would automatically devolve onto the UK post-Brexit. Importantly, this includes bilateral “mixed agreements” such as the trade agreements with Canada (CETA) and South Korea, to which the UK had been a party alongside the EU.
  • During the transition period, which is scheduled to expire by the end of this year, the EU and UK are negotiating their future relationship. EU law still largely applies to the UK under the terms of the Withdrawal Agreement. At the same time, the Withdrawal Agreement allows the UK to negotiate international agreements with other countries as long as these do not enter into force before the end of the transition and as long as the UK respects the principle of sincere cooperation (see Article 129 of the Withdrawal Agreement). One prominent example of such negotiations during this period are those between the UK and Japan for a free trade agreement (note that the EU and Japan have an Economic Partnership Agreement in force since February 2019).
  • Post-transition, the UK’s room for manoeuvre as a treaty-maker will to some extent depend on the shape of its future relationship with the EU. In view of both sides’ negotiating positions, a more or less ambitious trade or economic partnership agreement may result. A CETA-style agreement would leave the UK legally free to negotiate different trade agreements with partners around the world. However, the extent to which the UK will be able to disregard the rules set by the EU, which will remain its largest trading partner for the foreseeable future, remains an issue to be watched closely.

A global recalibration of treaty relations

Thanks to the Withdrawal Agreement, an abrupt rupture in the legal relations between the EU and UK as well as in the UK’s treaty relations with the rest of the world could be avoided. What is happening instead is a gradual shift from the UK’s status as an EU member state toward its post-Brexit future.

In addition to the lengthy Withdrawal Agreement, Brexit has prompted the creation of a sizeable amount of new international legal materials in the form of a series of continuity agreements, with new deals and an agreement on the future relationship with the EU in the making. Hence, despite all the uncertainty ahead, one thing is certain: Brexit and its aftermath will produce more, rather than less, international law.


Photo by Number 10 on Flickr.


NoteThe views expressed in this post are those of the author, and not of the UCL European Institute, nor of UCL.

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