As September 18—the day for the referendum on Scottish independence—approached, the “yes” side had gained tremendous momentum, and opinion polling indicated that the outcome was very much in question, though the “no” side held an edge. Only days before the vote, Cameron, Clegg, and Labour Party leader Ed Miliband jointly published in the Scottish newspaper Daily Record a pledge to increase powers for Scotland’s government if the referendum was rejected. In the event, some 85 percent of registered votes went to the polls and convincingly defeated the referendum, with about 55 percent voting “no” and about 45 percent voting “yes.”

In the wake of the referendum, having pledged to act quickly to make good on his promise to devolve more powers to Scotland, Cameron appointed an all-party commission to consider the details. At the same time, however, he wanted to bar Scottish MPs in the U.K. Parliament at Westminster from voting on issues that affected only England.

After the House of Commons voted 524–43 on September 26 to approve British participation in the U.S.-led air strikes against the Islamic State in Iraq and the Levant (ISIL, also called ISIS) insurgents in Iraq, Cameron stressed that the action would be limited to Iraq, that Britain would not attack ISIL in Syria, and that British troops would not be sent to participate in a ground war.

In the run-up to the British general election of May 7, 2015, Cameron addressed concerns regarding the scale of immigration to the U.K. by promising to seek a revision of the rules governing free movement of people as part of his plan to renegotiate Britain’s membership in the EU should he remain prime minister after the election. He also reiterated a pledge first made in 2013 to hold a referendum on continued British membership in the EU by the end of 2017 if reelected.

Right up to election day on May 7, 2015, opinion pollsters were predicting one of the closest contests in recent British history, with most polls putting the Conservative and Labour parties within one percentage point of each other. In the event, the pollsters were proved wildly wrong, as Cameron and his party won not only the largest share of seats in Parliament but also a slim overall majority, capturing 331 seats (a gain of 24 seats over the 2010 election), many at the expense of their soon-to-be former coalition partners, the Liberal Democrats, who watched their total representation fall from 57 seats to 8. At the same time, the Conservatives held off a challenge from the right by UKIP, which managed to win one seat, owing to Britain’s winner-take-all electoral system, despite a stronger showing in the raw vote nationally. Labour’s presence in Parliament fell from 258 seats to 232.

On November 10, 2015, in a letter to Donald Tusk, the president of the European Council, and in a speech, Cameron outlined his goals for a restructured role for Britain within the EU. In reinforcing his desire that Britain remain within the EU provided that the reforms that he sought were met, Cameron said that reaching that goal would be challenging but not “Mission: Impossible.” He sought reform in four key areas: (1) increasing competitiveness by reducing regulations on businesses, (2) limiting migration within the EU by allowing Britain to restrict tax credits and benefits for migrants, (3) extending the powers of national legislatures and exempting Britain from measures aimed at achieving “ever-closer-union,” and (4) creating protections for EU members that are not part of the single currency.

In the wake of the Islamist terrorist attacks in Paris on November 13, 2015, Cameron asked the House of Commons on December 2 to reconsider authorizing British air strikes in Syria against ISIL. More than 150 MPs spoke during the 10-hour debate on the measure, on the eve of which Cameron had stirred controversy by reportedly commenting that those who opposed British military intervention in Syria were “terrorist sympathizers.” Early in the debate Labour Party leader Jeremy Corbyn and other Labour MPs called on the prime minister to apologize for that remark; Cameron did not do so, though he did say that there was honour in voting for either side of the question. Cameron initiated the debate by asking,

Do we work with our allies to degrade and destroy this threat and do we go after these terrorists in their heartlands from where they are plotting to kill British people, or do we sit back and wait for them to attack us?

Corbyn, who staunchly opposed authorizing the bombing, as did most of his Labour colleagues, nonetheless freed members of his party to vote their conscience, and dozens of them joined Conservatives and others in voting for the measure, which passed 397–223.

At a summit meeting of the leaders of the member countries of the European Union in Brussels in February 2016, the European Council, reached at least compromise agreements on most of the reforms proposed by Cameron. Most notably, the British government would be permitted to limit benefits for migrant workers during their first four years in Britain, though this “emergency brake” could only be applied for seven years. Britain was also to be allowed to base benefit payments to the children of immigrant workers on the cost of living in the countries in which those children remained. Moreover, Britain would be exempt from the EU’s “ever-closer union” commitment, allowed to keep the pound sterling as its currency, and reimbursed for money spent on euro-zone bailouts.

When Cameron returned to London with the agreement in hand, he received the backing of most of his cabinet, announced that he would campaign for Britain to remain in the EU, and scheduled the referendum for June 23, 2016. There were, however, dissenters within the cabinet who made it clear that they would support Britain leaving the EU. Arguably the most-prominent Conservative proponent of “Brexit” (as the British exit from the EU was popularly known) was Boris Johnson, the popular mayor of London. Cameron, who had already announced that he did not plan to seek another term as prime minister, quickly entered into a war of words with Johnson, who was widely perceived to have designs on becoming the next leader of the Conservative Party.

In April 2016 Cameron came under fire when it was revealed that he, prior to becoming prime minister, had holdings in an offshore tax-haven-registered trust that had been created by his late father. That information came to light as part of a leak of more than 11 million documents (quickly dubbed the “Panama Papers”) from the secretive Panamanian law firm Mossack Fonseca, which exposed how a clutch of current and former world leaders as well as dozens of other politicians, public officials, and celebrities throughout the world had used tax havens to hide their wealth. Although Cameron had sold his shares in the trust before assuming office in 2010 and ostensibly had not violated any laws, the news was damaging for him because, as prime minister, he had taken a leading role in the fight against international tax evasion.

Although opinion polling on the eve of the referendum showed both sides of the “Brexit” question fairly evenly divided, in the event, some 52 percent of British voters chose to leave the EU, setting the stage for the U.K. to become the first country to ever do so. An emotional Cameron addressed the country from outside 10 Downing Street on June 24 to announce his intention to resign as prime minister by the time of the Conservative conference in October 2016 to allow his successor to conduct the negotiations on the British departure: “I don’t think it would be right for me to try to be the captain that steers our country to its next destination.” He emphasized his belief that there should be no hurry about triggering Article 50 of the Lisbon Treaty, under which the EU and the United Kingdom would have two years to negotiate their separation.

Johnson appeared poised to replace Cameron, but, in an abrupt turn of events, Johnson withdrew his name from consideration after he lost the crucial support of Justice Secretary Michael Gove, who chose to run for leader himself. After successive votes by Conservative parliamentarians, Home Secretary Theresa May and Energy Minister Andrea Leadsom emerged from the five-candidate field as the finalists. They were to be put to a vote by all party members with the results to come in September, but, when Leadsom unexpectedly dropped out on July 11, the party’s 1922 Committee, which was steering the leadership contest, declared May the new leader, effective immediately. As a result, Cameron’s tenure as prime minister came to a close even sooner than expected. Following Cameron’s final cabinet meeting on July 12, Health Secretary Jeremy Hunt said that across the cabinet there was “huge gratitude” for what Cameron had “achieved for the country and the way he’s changed the Conservative Party.” Cameron formally presented his resignation to the queen on July 13. On September 12, 2016, he also resigned from his seat in the House of Commons, saying:

In my view, the circumstances of my resignation as Prime Minister and the realities of modern politics make it very difficult to continue on the backbenches without the risk of becoming a diversion to the important decisions that lie ahead for my successor in Downing Street and the Government.