My article is intended as a primer on questions that Brexit raises with respect to EU law and UK constitutional law. Article 50 TEU states that ‘[a]ny Member State may decide to withdraw from the [European] Union in accordance with its own constitutional requirements.’ A state taking this decision must ‘notify the European Council of its intention’ under Article 50(2) TEU, setting in motion the withdrawal procedure.

I) The Decision to Leave the EU

The first step of withdrawal from the Union is a sovereign decision by the UK according to its own constitutional requirements. The article discusses these requirements in-depth. According to the (uncodified) UK constitution Parliament is sovereign and has ‘the right to make or unmake any law whatever’ (Dicey). The twentieth century might have brought some modifications of this doctrine, but did not change its substance. Parliament, however, has not taken any decision on Brexit. While it has passed a Referendum Act, it has failed to state the consequences of its outcome. This is in contrast to the referendum on the alternative vote system, for which Parliament stated how the result was to be implemented. The Brexit referendum was, accordingly, not legally binding.

There are two views on how the internal decision to trigger Article 50 TEU has to be reached. Either government itself can decide, exercising so-called prerogative powers, or parliamentary action is required. The royal prerogative power is exercised by or on behalf of the government. It is particularly ample in foreign affairs. Indeed, the UK acceded to the European Communities using the royal prerogative, even though Parliament had to align UK law with European law. There are convincing reasons, however, to doubt that the government may take the withdrawal decision based on the royal prerogative. First of all, withdrawal from the EU is hardly a decision in the field of foreign affairs, but rather a significant change in UK constitutional law, as EU membership is part of the constitutional setup of the UK (Thoburn v Sunderland City Council). Also, prerogative powers cannot, according to the Case of Proclamations and later case law, change statute law or repeal rights granted by statute. This, however, would be the effect of the government's notification of the decision to leave the EU.

Notification under Article 50 TEU triggers a two-year negotiation period that can be extended, but after which the EU Treaties cease to apply to the UK. In the article I describe what the effect of this will be and set out a typology of how different rights would be affected by withdrawal. I demonstrate that there is a category of rights which are granted by statute, but which will be lost even if Parliament would like to ‘rescue’ them, as they require action by the EU or by Member States, such as the European Parliamentary Elections Act 2002. Whatever UK statutes provide, Brexit will remove UK citizens’ right to vote in elections to the European Parliament. These issues are currently the subject of lawsuits filed in England and Northern Ireland, which are likely to be decided by the UK Supreme Court by the end of the year. While these questions pose serious challenges to the government’s approach, the same is not true with respect to devolution, as only constitutional convention demands the inclusion of the Scottish Parliament. 

II) The Process after Notification 

After notification of the intent to withdraw, Article 50(2) TEU provides for the negotiation of a withdrawal agreement, ‘taking account of the framework’ of the future relationship between the UK and the Union. There are thus two basic agreements that need to be negotiated. The more technical withdrawal agreement concerning, eg, unfinished structural funds and budget contributions, and the agreement concerning the future relationship, at times referred to as a ‘trade’ agreement.

After decades of close cooperation and integration, neither of these agreements will be easy to reach. Early statements that the withdrawal agreement must be negotiated before the ‘trade’ agreement, however, miss the mark. The wording of the provision requires negotiators to have at least an idea about the framework of the future relationship when the withdrawal agreement is negotiated. Practical considerations make it almost impossible to negotiate a withdrawal agreement absent any idea about the future relationship. In the article I describe the negotiation process and the internal conflict in the EU about which institution leads the negotiations. I caution against withdrawal without a new trade agreement, illustrating the consequences of what has been termed ‘hard Brexit’. Finally, I also discuss the regime during the withdrawal negotiations, suggesting that for practical reasons the UK needs to prioritize its negotiations with the EU. Other states will not be able to negotiate a free trade agreement with the UK without knowing first what the UK's legal position will be in this regard.

Dr Holger Hestermeyer is the Shell Reader in International Dispute Resolution at King's College London.