Britain is set to be the first ever member of the European Union to invoke Article 50 of the Lisbon Treaty.
Any country wishing to leave the EU is free to do so but must invoke Article 50 to negotiate their future relationship with the union.
The minimum time for the Article 50 process to be completed is two years, and Prime Minister David Cameron has said he will not invoke the article before he leaves office in October.
Once the article has been triggered, long negotiations will take place between Britain and EU representatives on their future relationship.
The article says: “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 EU.”
EU laws and rules will only cease to apply to Britain once all the processes in Article 50 have been completed.
When Article 50 has been invoked, British members of the European Union are banned from all EU discussions and decisions taking place about Britain’s membership.
The treaty states: “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.
It adds: “Unless the European Council, in agreement with the Member State concerned, unanimously decide to extend this period.”
There is no timescale of when to trigger Article 50 after a referendum, but EU members have urged Mr Cameron to do it as soon as possible ahead of their meeting on Tuesday.
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The article adds that Britain can apply to rejoin the EU whenever it likes but its acceptance would be subject to all member states agreeing to let it back in.
A Cambridge University lecturer claimed Article 50 was created to make things difficult for countries wanting to exit the EU.
Chris Bickerton states in his book The European Union: A Citizen’s Guide, that when the Lisbon treaty was drafted, they did not think anyone would ever wanted to leave the EU.
He wrote: “The Treaty of Lisbon was drafted with the idea that (Article 50) would not be used, and to make it pretty hard to exit in a smooth way.”
