David Cameron’s promise of an EU referendum in 2013 was designed to head off the apparent challenge to his party’s election hopes that was being posed by Nigel Farage’s Ukip. Although Ukip still did well in the 2015 election, the Conservatives won an overall majority.

Unfortunately for Mr Cameron, he lost the subsequent referendum, and his party was then tossed into years of turmoil over how the decision to leave should be implemented.