Editing Secession (section)

===European Union===
{{Main|Withdrawal from the European Union}}
{{See also|2016 United Kingdom European Union membership referendum}}

Before the [[Treaty of Lisbon]] entered into force on 1{{spaces}}December 2009, no provision in the [[Treaties of the European Union|treaties]] or [[European Union law|law of the European Union]] outlined the ability of a state to voluntarily withdraw from the EU. The European Constitution did propose such a provision and, after the failure to ratify the [[Treaty establishing a Constitution for Europe]], that provision was then included in the Lisbon Treaty.

The treaty introduced an exit clause for members who wish to withdraw from the Union. This formalised the procedure by stating that a member state may notify the [[European Council]] that it wishes to withdraw, upon which withdrawal negotiations begin; if no other agreement is reached, the treaty ceases to apply to the withdrawing state two years after such notification.<ref>{{Cite web|url=http://www.europarl.europa.eu/RegData/etudes/BRIE/2016/577971/EPRS_BRI(2016)577971_EN.pdf |title=Article 50 TEU: Withdrawal of a Member State from the EU|last=Poptcheva|first=Eva-Maria|date=February 2016 |website=europa.eu}}</ref>

On June 23, 2016, the United Kingdom voted to leave the [[European Union]] in a binding referendum voted for by parliament, and finally left the European Union on January 31, 2020.<ref>{{cite web |last1=Payne |first1=Adam |title=Business Insider |url=https://www.businessinsider.com/britains-new-parliament-votes-for-boris-johnsons-brexit-bill-2019-12 |website=businessinsider.com |publisher=Business Insider |access-date=December 20, 2019}}</ref> This is informally known as [[Brexit]].