But May is far from the first unelected prime minister. FullFact.com reports that since 1900 there have been 14 occasions on which 13 different Prime Ministers have come to power other than through a general election.
However, May might want to take note that – as history shows – newly appointed prime ministers have not always benefited from delaying calling a general election.
Here are the PMs who held out in the post-war period, with varying degrees of success:
Brown sparked a “Will he? Won’t he?” election mystery when he entered Downing Street after 10 years as Tony Blair’s Chancellor in 2007. Despite Tory claims that he lacked a mandate he abandoned plans to call a snap election and clung on to power for three years before David Cameron and the Conservative/Lib Dem coalition won in 2010.
Major was elected Tory leader in November 1990 after Margaret Thatcher’s dramatic fall from power. Despite calls for an immediate election from Labour leader Neil Kinnock, he took the UK into the Gulf War and survived an IRA assassination attempt before going to the polls in April 1992. He won and spent a further five years in power before Blair’s 1997 New Labour landslide.
Callaghan took over from Harold Wilson in 1976, after the latter resigned two years into his fourth term in office. At a time of heavy industrial unrest Callaghan took the country through the infamous Winter of Discontent before going to the polls in 1979. He was heavily defeated by Thatcher and Labour were out of power for the following 18 years.
Aristocrat Sir Alec was Prime Minister for 363 days, the second-shortest term in the 20th century. He was the Earl of Home and a Tory peer in the Lords when the party chose him in October 1963 to replace Harold Macmillan, who had retired through ill health. Sir Alec renounced his peerage and won a by-election for the safe Kinross and Perthshire West Commons seat, but then lost the the 1964 General Election to Wilson’s Labour.
The Old Etonian took over in 1957 when Anthony Eden resigned following the debacle of the Suez Crisis the previous year. “Supermac” led the country for two years before calling a General Election in 1959. He increased the Conservative majority by 20 at the expense of Hugh Gaitskell’s Labour.
Appointed Prime Minister in Britain’s “darkest hour” in 1940 to replace Neville Chamberlain, he led the Conservatives into the 1945 post-war election. The party was promptly thrashed by Clement Atlee’s Labour, who went on to create the NHS and the modern welfare state. Churchill eventually won an election in 1951 and was Prime Minister until 1955.