The British newspaper the Guardian called the referendum on June 23 2016 the ‘biggest political decision of the century’. British voters answered the question: ‘Should the United Kingdom remain a member of the European Union or leave the European Union?’
Moreover, particularly on the European continent, political leaders, thinktanks, scholars, business representatives and interested citizens are critically following the campaign for the referendum. On the European mainland various media has pointed out that leaving the European Union would be terrible for the (economic) stability and future of the EU. But would leaving the EU be legally possible when taken into account European as well as domestic law? This 'Library Special' tries to identify some –but not extensively- difficult legal talking points when the choice of the British people is to leave the EU.
It should be noted that the referendum is not legally binding. The Guardian of March 7th writes: ‘The British parliament still has to repeal the 1972 European Communities Act if the leave campaign wins, and ratify the Withdrawal Treaty. Members of Parliament could technically choose to ignore the referendum result and block the agreement, but it would be madness for politicians to attempt to go directly against a popular referendum result.’
In European law a provision is codified for Member States to withdraw from the European Union: Article 50 of the Treaty on the European Union (Hereafter: TEU) 
Paragraph 1 of art. 50 clearly states that the decision of withdrawal from the European Union is a sole prerogative of the Member State. It therefore, needs to be in accordance with its own constitutional requirements. After a decision is made by the British government it need to send a notification to the European Council. The leaders of the 27 other Member States of the European Union convene to discuss the notification and to draft a 'Withdrawal Treaty'. This particular treaty is concluded on behalf of the Union by the Council, acting by a qualified majority, after obtaining consent of the European Parliament. It is confirmed by the 27 remaining heads of state of the European Union.
If such a negotiation between the United Kingdom and the European Union is successful, the date of the United Kingdom's withdrawal from the European Union will then be the date of entry into force of the Withdrawal Treaty they will have agreed on together (first planned date 29 March 2019. Otherwise, if such a Withdrawal Treaty is not concluded, the withdrawal will automatically happen two years after the notification of the United Kingdom's decision to the European Council, according to art. 50 paragraph 3. During the necessary period for negotiating, signing and ratifying a Withdrawal Treaty between the United Kingdom and the European Union, the United Kingdom will remain a Member State of the European Union and continue to participate in its activities under the same conditions as before. The only legal exception is codified in paragraph 4 of art. 50 TEU which states that a representative of the United Kingdom will no longer participate in the discussions of the European Council or in the Council of Ministers as well as in their preparatory bodies (United Kingdom's Ambassador in COREPER, diplomats and civil servants in other bodies).
May's deal: the Withdrawal Agreement
Theresa May's deal was agreed with the EU last November. Its aim, broadly, was to allow the UK to formally leave today, while abiding by EU rules for a further 21-month "implementation period". This should have given the UK and EU breathing space while they hammer out the details of a future relationship. If lawmakers agree May's deal, it would mean the UK leaving the EU on May 22 and entering the implementation period. But if May can't pass her deal, then another way forward needs to be found. However, on 29 March 2019 -- the first date of 'Brexit' -- the British Parliament (House of Commons) has shown many 'NO' 's to the Withdrawal Agreement, even to options discussed and proposed within the Parliament. After another vote against the Withdrawal Agreement, Theresa May has resigned as Prime Minister.
Brexit: No deal
The House of Commons has said 'NO' with a large majority to a No Deal too. After all, Brexit may not mean Brexit, but no deal really does mean no deal. The UK would leave the EU on April 12 and become a third-party nation. It would trade with the world on terms set by the World Trade Organization and would fall out of all EU institutions. This would affect everything from medical supplies to air travel.
Wednesday 31 July 2019, Prime minister Boris Johnson has sent his most senior EU adviser and Brexit negotiator David Frost to Brussels to deliver in person his message that the UK will leave without a deal unless the bloc abolishes the Irish backstop: “The UK is leaving the EU on 31 October whatever the circumstances. We will work energetically for a deal but the backstop must be abolished. If we are not able to reach an agreement then we will of course have to leave the EU without a deal.”
Revoke Article 50
At the time of writing, it's unclear if the option of a holding second referendum will be discussed. Supporters of another public vote say that it's not a Brexit outcome, but a matter of process, and should be debated separately on its own merit. However, in the eyes of many, a second referendum is the only way the UK could credibly revoke Article 50, the process of leaving the EU, and remain in the bloc on its current terms. A big show of support for revoking Article 50 would be helpful for advocates of a second referendum. Whether they will get it or not is another issue entirely. Labour leader Jeremy Corbyn made clear that if a referendum was called on the Brexit deal negotiated by the incoming Conservative prime minister – or on whether to go ahead with a no-deal Brexit – Labour would support remain.
Norway Plus: Common Market 2.0
Norway Plus -- or Common Market 2.0, as some are now calling it -- is a very soft Brexit, in which the UK formally leaves the EU but remains very closely aligned to it. The "plus" part of this plan would be a customs arrangement between the UK and the EU that avoids a hard border on the island of Ireland. Under this plan, the UK would apply to join the European Free Trade Association, which would allow the UK to trade with the EU and other EFTA nations (Iceland, Liechtenstein, Norway and Switzerland) on similar terms to now. Via EFTA, the UK would also continue its membership of the European Economic Area, meaning it would retain access to the EU's single market. Under EFTA rules, the UK can still -- in theory at least -- strike its own trade deals while more or less maintaining trading ties with the EU. It will also result in minimal disruption to its world-class services industry. The UK would also leave the jurisdiction of the European Court of Justice in all areas other than those which affect the EEA. But as a member of the single market, the UK would have to abide by the four freedoms of movement: Goods, services, capital and people. That last one is a problem for Brexiteers, as it means the UK would not have full control over the number of people coming through its borders. The UK would have to continue making huge contributions to the EU, something that Brexiteers promised would end. Brexiteers don't like this Norway plus option because the UK would still need to abide to EU-law without any political participation in the decision-making process in Brussels.
And the unique customs arrangement envisioned by Norway Plus is unprecedented among EFTA membership, so there's no guarantee that it could be achieved, meaning the Irish border question is not necessarily answered. Also a separate customs union with the European Union will not be possible conform existing EFTA-regulations. And who says the United Kingdom will not act the same as it did within the EU in the past (Norway is afraid the UK will act as a kind of 'enfant terrible' within EFTA). So, while it looks a very clever plan, Norway Plus runs into many of the same problems as every other plan.
Canada-style free trade agreement
This hard Brexit option would lead to a free trade agreement between the UK and the European Union like Canada and the EU have agreed upon a few years ago: the Comprehensive Economic and Trade Agreement (CETA). CETA eliminates 98% of tariffs between Europe and Canada on certain goods and offers has access to much of the EU services market. The agreement is essentially a looser trading arrangement which removes many barriers between Europe and Canada. However, because Canada is not a member of the Customs Union or Single Market, customs checks still exist. The harder Brexiteers who want a looser relationship with Europe favor this plan, claiming that solutions will inevitably be found to deal with the Irish border question.
Soft Brexit: Permanent customs union
The main opposition Labour Party has faced wide criticism for not presenting a coherent Brexit plan. One thing we do know, however, is that it favors a permanent customs union with the EU, in which the UK has a say in future trade deals. A customs union is essentially a free-trade agreement between a number of countries who agree to share common external tariffs. That means no customs checks at borders. But because the EU is one large trading bloc, it also has a unified external trading policy, which EU member states can influence, but is ultimately run out of Brussels. This soft Brexit option might potentially get the most votes in favour in the British parliament, because the Irish border question does not come into play here and Labour and Conservative MP's will be able to negotiate a positive result here. This result might show similarities with May's deal, which contains a "backstop" plan of a single customs territory to handle the Irish border situation. Moreover there is no clear mechanism in which the UK could have a say in future EU trade deals.
For the Selective Bibliography please click here!
Article 50 of the Treaty on the European Union (Hereafter: TEU) reads as follows:
‘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.’
 Piris, J-C., Which Options would be available for the United Kingdom in the Case of a Withdrawal from the EU?, In: Britain Alone!: The Implications and Consequences of United Kingdom Exit from the EU, eds. Birkinshaw, P.J. and A.Biondi, Alphen aan den Rijn, Wolters Kluwer, 2016, pp 111-137.
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