By Niamh McCormack, pre-PhD candidate, Leiden University School of Law; research assistant, Grotius Centre for International Legal Studies.

On 9th September 2020, relations between the European Union (‘EU) and the United Kingdom (‘UK’) reached their lowest point since the UK’s 2016 decision to withdraw from the EU (‘Brexit’). This was precipitated by the UK government’s publication of draft legislation which would violate the terms of the EU-UK Withdrawal Agreement signed by both parties in January 2020, following three years of intense negotiation. The proposed legislation (the ‘Internal Market Bill’) would give UK government ministers the power to make unilateral decisions regarding the application of the Protocol on Ireland/ Northern Ireland (‘the Northern Ireland Protocol’) to the Withdrawal Agreement, disapplying a fundamental element of this treaty.

This ‘unilateral provocative act’ by the UK undermines key elements of the Good Friday Agreement, a peace settlement which largely ended more than thirty years of political violence in Northern Ireland. In response to the proposed legislation, Thomas Byrne, Ireland’s European Affairs minister, warned of the ‘completely unthinkable’ fall-out should the Internal Market Bill become law. In a statement on Internal Market Bill’s legal consequences, the UK Government acknowledged that the Bill would lead to a specific violation of the Withdrawal Agreement and amount to a breach of international law. This acknowledgement demonstrates the central role of international law in relations between Ireland, Northern Ireland, the UK and the EU.

The Good Friday Agreement: What is at stake?

The negotiation of the Good Friday Agreement represented an historic milestone in Northern Ireland’s journey towards peace. The negotiations involved community representatives from Northern Ireland’s unionist and nationalist communities, as well as representatives from the governments of Ireland, the UK and the United States. Since the signing of its two constituent agreements on 10th April 1998, the Good Friday Agreement has been considered as a model of how international negotiation and treaty law can serve as a tool to achieve peace.

The Good Friday Agreement serves both as a peace agreement and sets out an institutional framework for government in Northern Ireland. The treaty has three elements: (i) the creation of a Northern Irish government based on power-sharing between nationalist and unionist political parties; (ii) an agreement on the North-South relations on the island of Ireland which establishes mechanisms for cross-border cooperation; and (iii) provisions facilitating relations between Ireland and the UK. One key element of the Agreement is that it recognizes the right of people born in Northern Ireland to hold Irish citizenship, British citizenship, or both.

Fundamental to the effective operation of the provisions of the Good Friday Agreement are the common travel area arrangements (‘CTA’) between Ireland and the UK, which provide Irish and British citizens with certain rights, including: (i) freedom of movement and residence between Ireland and the UK; (ii) the right to work and to access social welfare services in Ireland and the UK; and (iii) the right to vote in Ireland and the UK (‘CTA Rights’). The maintenance of an ‘invisible border’ on the island of Ireland is fundamental to the realisation of these rights and thus for peace in Northern Ireland.

The text of the Good Friday Agreement was predicated on Ireland and the UK continuing as EU members and did not contemplate the possibility of either State leaving the EU. The UK Supreme Court in Miller (2019) endorsed the role of the EU in the architecture of peace and human rights in Northern Ireland, as well as in the UK as a whole. Integral to this architecture is a common understanding of human rights between Ireland and the UK, as well as the four principles of the European Single Market: free movement of capital, services, goods, and people. A principle impact of Brexit on these rights is the access of rights holders to enforcement at a supra-national level, with access to the Court of Justice being revoked. These considerations render the protection of the Good Friday Agreement a paramount consideration for any post-Brexit arrangements.

The Internal Market Bill and the UK Withdrawal Agreement

The Northern Ireland Protocol is a section of the Withdrawal Agreement, signed on 24th January 2020. The negotiation of this Protocol followed the failure of the ‘Irish backstop’ arrangement to secure the approval of the UK Parliament. The purpose of the Northern Ireland Protocol is to prevent the existence of an external EU border between Ireland and Northern Ireland, which would result in a ‘hard border’ on the island of Ireland, and is designed to allow goods to pass back and forth across the island of Ireland without any customs checks, as it operates currently. The Protocol imposes obligations on the UK to comply with decisions adopted by the European Commission regarding trade in Northern Ireland. Under the protocol, any necessary customs checks will occur when goods pass between Northern Ireland and the rest of the UK.

This compromise between the EU and UK ensures that EU VAT rules continue to apply to: (i) goods entering Northern Ireland from a non-EU country; and (ii) goods leaving Northern Ireland to a non-EU country. This effectively renders Northern Ireland both a part of the UK customs territory and the EU’s customs union, to obviate the need for customs checks on the island of Ireland. Where trade flows to Northern Ireland from the rest of the UK, EU customs entry formalities such as import declarations are to apply and goods must comply with all EU product regulations. Where trade flows from Northern Ireland to the rest of the UK, EU exit formalities such as export declarations are to apply.

The Internal Market Bill seeks to render the regulation of trade in England, Scotland, Wales, and Northern Ireland compatible. The Bill contains express provisions empowering ministers to set aside provisions of the Northern Ireland Protocol where they see fit. If the Bill passes into law, the UK Government will be empowered to: (i) remove any requirement for an export declaration where goods flow from Northern Ireland from the rest of the UK; and (ii) ‘set out its own interpretation’ of EU state aid rules for Northern Ireland. This would mean that the UK Government would not be effectively bound by EU state aid rules in relation to Northern Ireland, and would be contrary to the application of EU state aid rules to measures taken by the UK which effect trade in goods or electricity between the EU and Northern Ireland, as set out by the Protocol.

This repudiation of the terms of a legally binding international agreement brings the interaction between domestic and international law into sharp focus. The pacta sunt servanda principle, as codified by Article 26 of the Vienna Convention on the Law of Treaties, stipulates that every treaty in force is legally binding upon parties to it and must be performed by them in good faith. This principle applies regardless of the domestic decisions of a State party; although sovereignty means that a State may have the ability to act as it sees fit, this does not relieve the State of its pre-existing international legal obligations. The application of pacta sunt servanda to the Internal Market Bill shows the Bill to potentially violate two treaties to which the UK is party: the EU Withdrawal Agreement and the Good Friday Agreement. While state sovereignty is of paramount importance in international law, the repercussions of these violations would be grave. Any threat to peace in Northern Ireland, and to trade relations between the UK and the EU would have long-term economic and political effects for all parties. In summary, if a ‘no deal’ Brexit is to be avoided, and the existing political settlement in Northern Ireland is to be protected, then the UK must respect the international rule of law and perform its treaty obligations in good faith.


The introduction of the Internal Market Bill begins a further chapter in the saga of Brexit. Notwithstanding three years of negotiation, the Withdrawal Agreement and the Northern Ireland Protocol thereto is at risk of being violated less than a year after becoming effective. In addition to the political and economic ramifications for the UK’s future relationship with the EU, the Internal Market Bill becoming law would destabilise the existing peace on the island of Ireland, as it would result in the creation of a hard border between Ireland and Northern Ireland. The furore surrounding the proposed Bill highlights the importance of the international rule of law, as well as the dwindling effectiveness of claims of national sovereignty in avoidance of international obligations.