Whoever succeeds Mrs May when she goes will be what is now called “an unelected Prime Minister”. That’s to say, he or she will not be in Number 10 as a result of victory in a General Election. In the not very distant past this would have surprised nobody, been resented by few, and not held to make the new PM’s position somehow improper. Indeed only three Tory leaders since the 1914-18 war became Prime Minister for the first time with a popular mandate: Ted Heath in 1970, Margaret Thatcher in 1979, and David Cameron in 2010 – though that year’s election didn’t give him a majority in the Commons and he was only able to become PM in a coalition with the Liberal Democrats.
The other twentieth century Tory Prime Ministers – Bonar Law, Baldwin, Chamberlain, Churchill, Eden, Macmillan, Douglas-Home and Major – first became Prime Minister in the course of a parliament, and nobody thought this odd or improper. Major, alone of these, was elected party leader, in his case by an electorate restricted to Tory Members of Parliament. Ted Heath had been the first Tory leader elected in this way and Margaret Thatcher would be the second when she challenged Heath. All the others emerged after what came to be called “the customary process of consultation”. Actually the process changed from time to time, and might not have been correctly termed “customary”.