欧盟成员国退出欧盟的权利在《里斯本条约》中首次被提出。此前，退出欧盟的可操作性是备受争议的。

《里斯本条约》于2007年12月13日由欧盟各国首脑在里斯本签署，2009年12月正式生效。该条约在原《欧盟宪法条约》的基础上修改而成，被视为“简版”的《欧盟宪法条约》。

The right of a Member State to withdraw from the European Union was introduced for the first time with the Lisbon Treaty. The possibility of withdrawal was highly controversial before that.

《里斯本条约》第五十条规定的退出程序适用于英国脱欧是毋庸置疑的。

英国一开始也曾经考虑过其他的可能性，但是主流意见是根据第五十条规定的程序来退出欧盟，其后英国政府也基本接纳了这一观点。

《里斯本条约》第五十条：

1.任何欧盟成员国都可以根据本国的宪法规定自主决定退出欧盟。

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

2.成员国应当将拟脱欧的计划通知欧洲理事会。根据欧洲理事会的指导方针，欧盟应当同拟脱欧国磋商达成协议，解决脱欧前的准备工作，并进一步考虑该国与欧盟未来关系的框架。该协议的磋商谈判必须以《欧洲联盟运作条约》第218条第（3）款为依据。理事会应当在获得欧洲议会同意后代表欧盟，经特定多数通过后签署该协议。

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.自脱欧协议生效之日起，或自第2款所述通知生效之日起两年后，本条约将不再适用于该拟脱欧国，但欧洲理事会与该拟脱欧国一致决定延长这一期限的除外。

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.在本条第2、3款的规定中，该拟脱欧国在欧洲理事会的代表或该脱欧国在欧盟理事会代表均不得参与欧洲理事会或欧盟理事会就脱欧事项的讨论或有关决定。

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.

 5. 若已脱欧的国家请求重新加入欧盟，则必须依照本法第49条所规定的程序进行。

If a State which has withdrawn from the Union asks to rejoin, its request shall be subject to the procedure referred to in Article 49.

《里斯本条约》规定了2年的谈判期限，英国政府于2017年3月29日启动脱欧程序，所以很多报道都说2019年3月29日是英国脱欧的最后期限。但是因为英国议会对于提交的脱欧方案不买账，英国议会迟迟不通过首相提交的的脱欧方案，所以到直到现在，都已经4月底了，英国脱欧 一拖再拖。

现在是2019年4月底，也就是说，2年的谈判期限已经经过了，这回产生什么法律后果呢？

除非欧盟其他27个成员国一致同意延迟谈判期限，英国将不能参与到脱欧的谈判中，换句话说，如果其他27个欧盟成员国不能一致同意延长英国脱欧谈判，英国只能坐等欧盟对英国脱欧做出的决定。

但是，欧盟4月10日表示，欧盟已同意将英国脱欧的最后期限延长至10月31日，所以，英国还是可以参与到脱欧谈判的。

英国在脱欧期间还享有成员国权利吗？还可以在欧盟议会中选举代表吗？

英国还可以会参加欧洲议会选举（European Election），英国仍拥有欧盟正式的会员权利和义务。

如果英国脱欧后还能重新加入欧盟？

答案是可以，那么按照什么样的程序加入呢？

正常的申请加入欧盟程序，就像新的成员国要加入欧盟一样。

Lisbon Treaty：里斯本条约

European Council：欧洲理事会

the State in question：所述国家 

Member State：成员国

set out：解决、得出（方案）

withdraw from:退出

in accordance with：根据

on behalf of：代表

represent：代表

In the light of：根据，鉴于

For the purposes of：为了..目的

conclude an agreement ：达成协议                   

unanimouslydecide：一致决定

be subject to:遵从

refer to:参照