If Britain voted to leave the EU, what would happen next?

Brexiters play down the difficulties of renegotiating trade and other deals, but the process of withdrawal could take years

For the first half century of its existence, joining the club of nations that became the European Union was, in legal terms at least, forever. Once inside, there was no way out.

But the Lisbon Treaty, which came into force in 2009 to streamline the EU's working practices after it had expanded to include the former communist states of eastern Europe, also signposted the exit for the first time.