Until 2007, joining the European club was assumed to be a one-way ticket. There was no formal mechanism in the rules setting out how a state could leave the European Union. But there is now. Article 50 of the Lisbon Treaty sets out a road map. It boils down to a couple of deceptively simple steps. The prime minister would have to write a letter to the President of the European Council notifying him of the intention to leave. The council would appoint a lead negotiator and a negotiating team. A two-year window to negotiate a withdrawal treaty would follow - if Britain decides it wants one. The window could be expanded by a year if necessary. Any withdrawal treaty would be concluded by the European Council through qualified majority voting and then ratified by the European Parliament and the Westminster Parliament. Full article link below, I didn't realise anyone had thrown out before...apparently Greenland voted out in 1982. http://www.bbc.co.uk/news/uk-politics-35233683