Constitutional expert on possible second EU referendum

Constitutional expert Dr Alan Renwick says "there is a process that takes place once a country decides that it's going to leave the European Union."

He said that in the event of a vote to leave the EU, it would be "political untenable" for the prime minister not to invoke Article 50 to trigger the start of negotiations for the UK to leave the EU.

The deputy director of the Constitution Unit at University College, London, was speaking to Martha Kearney on Radio 4's The World at One