LONDON — Britain is scheduled to have a new prime minister by early September, less than three years since the incumbent, Boris Johnson, led his Conservative Party to its biggest election victory in decades.
There are two contenders: Mr. Johnson’s former top finance official, Rishi Sunak, and Liz Truss, the foreign secretary.
But it won’t be a general election that decides who gets the job. Instead, the selection process is playing out inside the Conservative Party.
Here’s a guide to how it works, who could win and what might happen next.
In Britain’s parliamentary system, the leader of the majority party is in charge.
It is hard to get rid of a British prime minister, but far from impossible. The job goes to the leader of the political party with a parliamentary majority. The party can oust its leader and choose another one, changing prime ministers without a general election.
Three of Britain’s last four prime ministers, including Mr. Johnson, came into office between elections. The new prime minister may then choose to face the voters — in 2019, Mr. Johnson did so within months — but there’s no obligation to call a new general election until five years after the last one.
Boris Johnson’s party forced him to step down, with a shove from a potential replacement.
Mr. Johnson’s position started to weaken late last year, with a series of scandals involving parties during Britain’s coronavirus lockdown that eventually brought him a fine and a stinging official report. In June, he survived a no-confidence vote among his party’s lawmakers.
The next month, however, brought a new scandal, with the departure of Chris Pincher, a deputy chief whip, who was responsible for keeping Conservative lawmakers in line. Mr. Johnson had placed him in the job despite accusations of inappropriate behavior. Ministers and other officials denied on Mr. Johnson’s behalf that he had been aware of those accusations, only for successive accounts to rapidly unravel.
On the evening of July 5, Mr. Sunak resigned, alongside another top minister, Sajid Javid, the health secretary. A flood of further resignations followed, with more than 50 members of Parliament quitting cabinet roles or other official positions by July 7, including some appointed to replace those who had already resigned.
The Fall of Boris Johnson, Explained
Later that day, Mr. Johnson announced that he would resign, acknowledging in a speech that it was clearly “the will of the parliamentary Conservative Party” that he step aside.
His lawmakers set the terms of the contest to replace him.
When Mr. Johnson resigned as leader of his party on July 7, he said he would remain as prime minister until the Conservatives had chosen a new leader. His two most recent predecessors, David Cameron and Theresa May, both took that approach when they resigned.
But the timetable for the leadership contest is not in Mr. Johnson’s hands: It is set by backbench Conservative lawmakers through a body called the 1922 Committee.
The broad outlines of the two-stage process remain constant. First, Conservative lawmakers hold a series of ballots among themselves to whittle the number of contenders down to two.
Then there’s a ballot on the final choice among the party’s entire dues-paying membership. These are members of the public who pay a standard annual subscription of 25 pounds, about $30, and it’s estimated that there are about 160,000 of them.
Eleven lawmakers sought to run this time, with the final two — who ended up being Mr. Sunak and Ms. Truss — revealed on Wednesday after five rounds of voting.
Party members will be able to question Mr. Sunak and Ms. Truss at a series of meetings around Britain over the summer, but the later sessions may matter less; voting, by post and online, opens in early August.
The result is then due on Sept. 5. That would give the new prime minister time to prepare for a major televised speech at the Conservative Party’s annual conference in October.
Rishi Sunak was lawmakers’ top pick. But he may struggle in the final vote.
Through all five rounds of voting by lawmakers, one candidate remained in the lead: Mr. Sunak, who as chancellor of the Exchequer was the top finance official for most of Mr. Johnson’s time in Downing Street.
Were he to win the final vote, Mr. Sunak, 42, would be Britain’s first prime minister of color — though there was a premier with Jewish heritage, Benjamin Disraeli, as long ago as 1868. For some time, Mr. Sunak has been considered a favorite to take the job.
Polling suggests, however, that he is struggling to win over party members.
Mr. Sunak took up his post as chancellor in 2020, as the coronavirus was reaching Britain, and he gained popularity through his calm handling of its economic impact as it became a pandemic, including through a furlough program that paid companies to sustain nearly 12 million jobs during lockdown.
But this year, he had a fall from grace of his own. Like Mr. Johnson, he was fined for attending a party that broke coronavirus regulations, and he has also faced damaging reports around the tax status of his wealthy wife.
In the final vote, he may also suffer from his association with tax increases and Britain’s cost-of-living crisis, as well as his part in pushing out Mr. Johnson, who retains a following among party members. One minister loyal to Mr. Johnson, Jacob Rees-Mogg, has declined to deny describing Mr. Sunak as a “socialist” during a cabinet meeting.
Liz Truss is speaking for the party’s right, despite a centrist past.
Liz Truss, the foreign secretary, remained in the government during the wave of resignations that felled Mr. Johnson. She took second place only in the final round of the lawmakers’ ballot, consolidating support from several defeated candidates on the party’s right to overhaul Penny Mordaunt, a middle-ranking minister who was presenting herself as more of a clean break with the Johnson years.
Once a student activist for a smaller, centrist party, the Liberal Democrats, Ms. Truss, 46, campaigned for Britain to remain in the European Union during the 2016 Brexit referendum — a key dividing line for the many Conservative members who, like Mr. Sunak, voted to leave.
But she has remade herself as a champion of Brexit causes, pursuing aggressive negotiations with the European Union over trade in Northern Ireland. In this contest, she has also promised to pursue rapid tax cuts, to be funded by repaying pandemic debt over a longer period.
That’s a point of distinction with Mr. Sunak, who has described the idea as “fantasy economics” and is likely to present himself as a responsible steward of the nation’s finances during a period of extreme stress.
Ms. Truss’s campaign has not had as smooth a start as Mr. Sunak’s, analysts said. On Wednesday, after winning through in the final lawmakers’ ballot, she briefly posted on Twitter that she was ready “to hit the ground from day one,” forgetting to add “running.” Even so, pollsters and oddsmakers identify her as the favorite in the membership vote.
Whoever wins has up to two years, with a tricky road ahead.
Whichever candidate emerges victorious in September, things look sticky for the government. Inflation is surging, interest rates have risen and household bills are soaring, with another hefty step up in domestic energy prices scheduled for October.
But the new incumbent will also have one of the most significant advantages given to governing parties in British politics: the ability to choose the date of the next general election.
The last available moment would be January 2025. Going much sooner is an option, to capitalize on early popularity and pre-empt further bad news, but it would be a dangerous one. Mr. Johnson’s snap election produced a landslide victory, but Mrs. May, his predecessor, called an early election with a double-digit poll lead, only to lose both her parliamentary majority and her authority.
And the circumstances are far less favorable now. In recent days, the Conservatives have slipped 10 or more percentage points behind the opposition Labour Party in most opinion polling, and responses to pollsters’ hypothetical questions suggest neither leadership candidate would make a drastic difference. Labour, however, has lost previous elections after holding similar or larger midterm leads.
If the next incumbent can navigate the choppy economic waters ahead, it could still be a fair few years before Britain has yet another prime minister.