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Signed by European Union (EU) member states in December 2007, and entered into force in December 2009, the Lisbon Treaty was an update to the Maastricht Treaty from 1993 and amended the two treaties which formed the constitutional basis of the EU.

Article 50 of the Lisbon Treaty is a five-point plan devised should any nation decide to leave the EU – hence its relevance here. It sets out a two-year exit process, during which time it will be constantly negotiated with the 27 other members of the EU.

Once David Cameron decided on activating Article 50, and there has been on timeframe set on this, Britain effectively loses its seat at the decision-making table.

The five points of Article 50 effectively mean:

1. A member state may withdraw from the EU “in accordance with its own constitutional requirements”
2. It must notify the European Council of this plan, after which it will negotiate and conclude an agreement on the terms of withdrawal
3. The treaties formally governing the member state no longer remain applicable to the exiting nation from the date of entry into force or the withdrawal agreement or two years after notification
4. The leaving country’s European Council representative does not participate in any meetings or discussions concerning its exit process
5. Should a country which has exited the EU decide it wants to rejoin, procedures from Article 49 are consulted

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The process of enacting Article 50 has never been tested, as membership of the EU has so far been one way traffic. From the founding members, Belgium, France, Germany, Italy, Luxembourg and the Netherlands, through Britain, Ireland and Denmark’s admittance in 1973, to the newest member in the shape of Croatia, the EU has only ever become bigger.

Have a look at our other Brexit coverage:

• Four EU business laws that have a dubious future after Brexit
• “Half-hearted ambivalence” from Jeremy Corbyn as Angela Eagle also quits
• Mark Carney shows now is the time for stable thinking

Some analysts predict that Cameron’s decision to defer the activation of Article 50 to his successor leaves the door open for Britain to remain in the EU. It is entirely up to the exiting country, in this case the UK, to decide when the ball starts moving on Article 50 – even if pressure for a decision does come from the remaining members.

As Kenneth Armstrong, professor of European law at Cambridge University, said in The Guardian: “There is no mechanism to compel a state to withdraw from the European Union. Article 50 is there to allow withdrawal, but no other party has the right to invoke article 50, no other state or institution. While delay is highly undesirable politically, legally there is nothing that can compel a state to withdraw.”

One interesting aside is that, without triggering Article 50, Britain may find it hard to negotiate with centralised EU powers – as its long-term future has not been indicated. Furthermore, a new agreement with the EU wouldn’t actually require agreement from all member states.

However, there is one thing for sure. There is no way back once Article 50 is in motion.

A 500-word summary of the short and long-term Brexit business implications