On a hot Monday morning in June 2026, Sir Keir Starmer stood at a lectern outside 10 Downing Street and, voice cracking with emotion, announced he was resigning as Labour leader and prime minister. It was a moment that set in motion a familiar but often misunderstood process: the selection of a new prime minister without a general election. For UK readers watching the news, the central question is simple: who decides who becomes prime minister, and how does it happen?
The short answer is that the prime minister is not directly elected by the public. Instead, they are the leader of the political party that wins the most seats in a general election. When a prime minister resigns, their party chooses a new leader, and that person automatically becomes prime minister – provided their party still commands a majority in the House of Commons. Sir Keir became prime minister on 5 July 2024 after Labour's landslide general election victory. His departure means Labour must now pick a successor, who will take over as head of government without a national vote.
“Explains how a UK prime minister resigns and is replaced, using Starmer's departure as example.”
In Sir Keir's case, the pressure had been building for months. His approval ratings were poor, and a damaging by-election defeat in February 2026 – where Labour lost a formerly safe seat to the Greens after he blocked the then Greater Manchester mayor Andy Burnham from standing – turned local elections in May into a leadership litmus test. The results were devastating, prompting several ministers to resign. A long-simmering row over defence spending led to the resignation of Defence Secretary John Healey. Then Andy Burnham won the Makerfield by-election convincingly last week, defeating Reform UK and clearing his path to return to Westminster. Sir Keir initially insisted he would fight any leadership challenge, but after a weekend of soul-searching with his wife Victoria at Chequers, he concluded that Labour MPs wanted someone else to lead them into the next general election.
The process for replacing a Labour leader – and therefore the prime minister – is set out in the party's rulebook. Candidates for the leadership must be nominated by at least 81 Labour MPs, plus either 32 of Labour's 634 local branches or three affiliated organisations (including two trade unions). Nominations open on 9 July and close on 16 July, when Parliament breaks for summer recess. If only one candidate clears this threshold, they become leader automatically and can enter Downing Street as prime minister as early as mid-July. If more than one qualifies, a ballot of party members and affiliated trade union supporters is held, with the winner announced before Parliament returns on 1 September. Sir Keir said he will remain prime minister until his successor is chosen.
Andy Burnham is the clear frontrunner. He confirmed his candidacy on Monday and immediately received a boost when former Health Secretary Wes Streeting, his most likely rival, ruled himself out and endorsed Burnham. No other Labour MP has yet declared, raising the possibility of an uncontested coronation. If that happens, Burnham could become the UK's seventh prime minister since 2016 – and the shortest-serving Labour prime minister in history will have been replaced by a man who was an MP only days earlier.
Q: How is a new prime minister chosen when the incumbent resigns? The ruling party follows its internal rules to elect a new leader. That person automatically becomes prime minister, as long as the party still holds a majority in Parliament. There is no general election unless one is called.
Q: Can Andy Burnham become prime minister without a general election? Yes. If he wins the Labour leadership contest, the Queen will appoint him as prime minister. He would then lead the government until the next general election, which must be held by August 2029 at the latest.
Q: Why did Keir Starmer resign after less than two years as PM? He faced mounting pressure from Labour MPs after poor election results and a series of resignations from his cabinet. His authority was fatally weakened when a by-election defeat and internal rebellions made clear he no longer had the confidence of his parliamentary party.
What happens next will be determined by Labour's leadership timetable. Nominations open on 9 July and close a week later. If only Andy Burnham stands, he could become prime minister within days. If there is a contested election, the new leader will be chosen by party members and affiliated union supporters before September. The UK will have its seventh prime minister in a decade, and attention will quickly turn to whether Burnham can restore Labour's fortunes before a general election that must come by August 2029.