Brexit: How Exactly Will Britain Leave The EU?

By Laura Bassett


On June 23, 2016, the United Kingdom held a referendum on their European Union membership, which was commonly called the “Brexit.”[1] The (ultimately successful) people who voted to “leave” were mostly motivated by concern over the nation’s seemingly decreased sovereignty, while those who voted to “remain” were highly motivated by the trade and economic benefits of being a member of the bloc.[2] The UK joined the European Union in 1973, but it held a referendum just two years later on continued membership.[3] The 1975 referendum, unlike its recent incarnation, showed an astounding 67% of voters choosing to remain in the European Union.[4] The 2016 vote has already been called into question, though, with voters declaring that they “didn’t think [their] vote was going to matter too much because [they] thought [the U.K. was] just going to remain” and still others noting that, if they had the ability to vote again, they would vote to “remain” instead.[5]

Governing Law

The law that will govern the Brexit, should it happen, is Article 50 of the Treaty of Lisbon, which states:

1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.

2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. That agreement shall be negotiated in accordance with Article 218(3) of the Treaty on the Functioning of the European Union. It shall be concluded on behalf of the Union by the Council, acting by a qualified majority, after obtaining the consent of the European Parliament.

3. The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.

4. For the purposes of paragraphs 2 and 3, the member of the European Council or of the Council representing the withdrawing Member State shall not participate in the discussions of the European Council or Council or in decisions concerning it.

A qualified majority shall be defined in accordance with Article 238(3)(b) of the Treaty on the Functioning of the European Union.

5. If a State which has withdrawn from the Union asks to rejoin, its request shall be subject to the procedure referred to in Article 49.[6]


To satisfy Article 50(1), the Members of the British Parliament must pass an Act of Parliament consenting to the departure from the European Union.[7] As prominent members of the U.K. Constitutional Law Association have pointed out, this is where the MPs could override the departure by simply voting down the Act of Parliament.[8] As Oxford Associate Professor of Constitutional Law Nick Barber notes, though, the MPs would have to be politically brave enough to risk voting down the measure in spite of the outcome of the referendum.[9] There is also the possibility that the new Prime Minister, Theresa May, could make an Article 50 declaration without having the MPs vote on it; however, that decisions would very probably be subject to judicial review, especially since a use of what is called the “Royal Prerogative” cannot be used to contradict an Act of Parliament; this precedent was created in 1610 by Sir Edward coke, and experts suggestive that it could be used to override any Royal Prerogative that would be in contradiction with the 1972 European Communities Act and the European Parliamentary Elections Act of 2002.[10]

Assuming that the MPs do not go against the results of the referendum, the next step would be a declaration of intent to the European Council, after which negotiations would commence to decide the trading relationship between the Union and the departing state.[11] From this point, the treaties will cease at the completion of a Withdrawal Agreement or two years from notification, barring an action by the European Council to prolong the time frame.[12] With these mechanisms in place, it appears that the biggest hurdle is complying with the U.K.’s constitutional requirements from leaving the E.U.; once that Act of Parliament has been passed, the Treaty of Lisbon has a strict timeline that can only be prolonged, not terminated.[13]

An important thing to note, especially with all the dissention amongst the voters,[14] is Article 50(5) of the Lisbon Treaty, which redirects to Article 49 in the event of a state’s wish to rejoin the Union.[15] While there are several conditions for admission (or in the U.K.’s case, readmission) to the European Union, the European Council must specifically agree on condition for admission, per the last sentence of Article 49.[16] However, upon readmission, the U.K. might not be granted the same opt-out that they currently have in regards to adoption of the Euro.[17] Currently, only the U.K. and Denmark have ‘opt-outs from the European Monetary Union (a.k.a. Eurozone), and every country that has joined since 1999 has been required to eventually ascend to the Eurozone, once the ascension criteria has been met.[18] Some experts speculate that further integration is necessary for the continued existence of the European Union, and if that is true, the EU will probably not be willing to allow the readmission of the U.K. without an agreement to adopt the Euro instead of the Pound as their currency.[19]

* * * * *

[1] Brian Wheeler & Alex Hunt, The UK's EU Referendum: All You Need to Know, BBC News (June 24, 2016),

[2] Steven Erlanger, ‘Brexit’: Explaining Britain’s Vote on European Union Membership, N.Y. Times (June 21, 2016),

[3] Id.

[4] Id.

[5] Tara John, These Brexit Voters Think They Have Made a Horrible Mistake, Time (June 24, 2016),


[6] The Lisbon Treaty,

[7] Adam Lusher, Brexit can still be blocked, say constitutional lawyers, Independent (June 28, 2016),

[8] Id.

[9] Id.

[10] Id.

[11] Lisbon Treaty, supra note 6, at Article 50(1), 50(2).

[12] Id. at 50(3).

[13] Id.

[14] John, supra note 5.

[15] The Lisbon Treaty, supra note 6.

[16] The Lisbon Treaty, supra note 6 at Art. 49,

[17] Andrew Lilico, After 2020, All EU Members Will Have to Adopt the Euro, The Telegraph (July 1, 2014, 5:00 PM BST),

[18] Id.

[19] Id.