Cameron, who supported Britain's continued membership of the EU, announced his resignation on 24 June, saying that he would step down by October.

Withdrawal of the United Kingdom from the European Union During the 2015 general election campaign, David Cameron, then leader of the Conservative Party and prime minister, announced that he would not seek a third term; he was therefore expected to stand down before the following general election – at that time, expected to occur in 2020 – although he spoke of serving a full term.

[2] Following a manifesto commitment, Cameron and the Conservative Party introduced legislation for a referendum on the UK's membership of the European Union, which was held on 23 June 2016.

There was speculation during the campaign as to whether Cameron would resign if Leave won, but on the day of the referendum, both Leave- and Remain-supporting Conservatives called for him to stay whatever the result.

He said that he would continue in post while the leadership election was ongoing, with the new leader to be in place in time for the party conference in October.

Johnson's candidacy was expected to be supported by Michael Gove, the two having worked together for Leave through the referendum campaign, as well as by Andrea Leadsom.

[9][10] The Telegraph stated that Gove's actions in undermining Johnson's leadership aspirations constituted "the most spectacular political assassination in a generation.

[12][13] Some of Johnson's allies subsequently began shifting their support to May, because they perceived a "systematic and calculated plot" by Gove to remove their candidate from the race.

[14] By 5 July 2016, Gove was in a distant third place in the leadership race based on the number of endorsements received from other MPs.

[15] The initial days of the campaign remained overshadowed by the fallout from Gove's entry into the race and Johnson's departure.

Gavin Williamson – later to be appointed Chief Whip by May – was her parliamentary campaign manager and responsible for rallying this support, together with a small group of MPs including Julian Smith, Kris Hopkins, Simon Kirby, Karen Bradley and George Hollingbery.

[17] Leadsom had approached the Johnson campaign with a proposed deal not to run in exchange for being made one of his top three ministers.

[19] The five candidates also rejected the idea of calling a second referendum on British withdrawal from the EU, pledging to take the UK out of the Union, although on different timeframes.

[19] Among the key issues that emerged during the Conservative leadership campaign were: An editorial in The Guardian noted that the Brexit-dominated leadership campaign presented a danger that the next prime minister would be chosen on this basis at a time when several major domestic issues would also demand the prime minister's attention, such as the disputes between the government and unions representing teachers and junior doctors.

[31] Meanwhile, Crabb, after his candidacy had ended, was reported to have been sexting a woman despite being married and stressing family values in his campaign.

[35][36][37] Nominations for the leadership are invited by the Chairman of the 1922 Committee (Graham Brady at the time), acting as Returning Officer for all stages of the election.

A ballot paper is produced and issued to all Conservative Members in the House of Commons, who indicate one choice from the candidates listed.

Fifth-placed candidate Fox was knocked out of the race, and Crabb withdrew following scandalous revelations about his private life;[39] both endorsed May.

[42] She was confirmed as leader; David Cameron tendered his resignation as prime minister on 13 July, with May accepting the Queen's invitation to succeed him shortly afterwards.