Article 50 is part of the Treaty of Lisbon - an agreement signed by all states of the European Union - and outlines the rules that a country must follow if it wishes to exit the EU. Prior to the treaty becoming law in December 2009, there was no official process for this to happen.
It was written by the Scottish cross-bench peer Lord Kerr of Kinlochard, who has said since the Referendum that he thought that if it was ever used it would be if there was a coup in a member state and the EU suspended that country's membership - not for Brexit.
Only five paragraphs long, Article 50 states the below:
- Any EU member state may decide to withdraw from the Union.
- It must notify the European Council of its decision and negotiate the terms and arrangements of its exit from the EU.
- Once the notification has been made (or "triggered") there are then two years to reach an agreement about the state's departure and for it to formally leave. This timescale can be extended but only if agreed unanimously by the European Council (i.e. all member states) and the country concerned.
- The withdrawing state cannot take part in internal EU discussions and decisions about its departure. An exit deal must be approved by a "qualified majority" of the EU members, as well as receiving backing by MEPs.
- If a state that has left the Union wishes to rejoin, the request will be dealt with under terms outlined in Article 49 and it must apply like any other country.
So what precisely does that mean for us?
No state has left the EU before, so putting the procedure into practice is as uncertain as what will happen afterwards. Last November, it was ruled by the High Court that MPs must vote on triggering Article 50 before the government is allowed to do it. The Supreme Court upheld the ruling, a Notification of Withdrawal Bill was published, and the House of Commons voted in favour of giving the prime minister the power to begin the process with a majority of 498 to 114. Theresa May has said that she plans to trigger Article 50 no later than the end of March 2017, meaning that officially Britain should be out of the EU by April 2019 - although many believe it could take much longer. The complex terms to be negotiated once it is triggered are expected to include new trade agreements, cross-border security, and the rights of EU citizens living in the UK and those of British nationals abroad.Gina Miller On Justice, Brexit And Being "Hated"