It is hard to see Mr Cameron campaigning for anything other than to stay in. Most businesses and the City of London want to remain. Mr Cameron knows that the uncertainties from an Out vote would deter foreign investment. And it would also surely lead the Scottish National Party (SNP) to demand and probably win a second referendum on independence. A vote to leave the EU could thus be a precursor to the break-up of the United Kingdom itself.

The EU referendum will also be crucial for the conference’s second big subtext: the party leadership. Mr Cameron confirmed that he was not going to fight the next election, in 2020, as leader. That fuelled speculation over his successor and jockeying among the candidates. Mr Osborne remains the favourite but, as Mr Cameron was careful to point out, favourites often stumble. Mr Osborne’s chances will depend on the success of the economy, but he, too, will want the referendum to be in favour of staying in.

Were the Outs to win, Mr Cameron would surely have to resign (as Alex Salmond, the SNP leader, did after the 2014 Scottish referendum). The leadership could then go to a more Eurosceptic candidate such as the business secretary, Sajid Javid, or the justice secretary, Michael Gove. Ms May and Mr Johnson openly touted their leadership (and Eurosceptic) credentials this week—though only Mr Johnson won a standing ovation following a mention in Mr Cameron’s speech. The sad irony for Mr Cameron is that just at his greatest moment of triumph the Conservatives should stop listening to him and instead take note of those who would replace him.