Keir Starmer has resigned as leader of the governing Labour Party in Britain and will remain in office only as a caretaker prime minister until Labour chooses his successor. That leadership election is expected to conclude by mid-July, or before Parliament rises for the summer recess. In the formal language of Westminster, this is an orderly transition. In political reality, it is a collapse.

Starmer has become the latest in a succession of prime ministers not removed by voters but pushed out by his own party. Cabinet ministers and Labour Members of Parliament moved against him after concluding that he had become an electoral liability. The party that had marched into office with a huge majority in July 2024 decided, less than two years later, that the man who delivered that majority could no longer be trusted to defend it.

The mutiny had three immediate causes.

The first was electoral humiliation. Labour’s losses to Reform UK in recent local and municipal contests shattered confidence in Starmer’s ability to hold back an assault from the new right of British politics. Reform UK, an upstart part of the political right, has transitioned from a peripheral pressure group on the edge of British politics to the party setting the pace of Britain’s rapidly evolving political landscape.

The second was the Mandelson scandal. Starmer’s appointment of Peter Mandelson as United Kingdom (UK) ambassador to the United States damaged his claim to clean, serious, competent government given Mandelson’s past ties to Jeffrey Epstein.

The third was the recent Makerfield by-election. Andy Burnham, the former mayor of Greater Manchester, won the seat and proved that another Labour figure could defeat Reform UK in a direct fight.

His victory last week changed the internal balance of Labour politics. Burnham took more than 55.0% of the vote and won by more than 9 000 votes. More importantly, he did so while Labour was bleeding support elsewhere. In defeating Reform UK he gave Labour members a glimpse of how it might be contained – providing the final impetus for the party to jettison Starmer.

This is the extraordinary arc of Starmer’s premiership. He began with a landslide and ended as a caretaker. Labour’s July 2024 victory looked overwhelming on paper, but it was always more fragile than the seat count suggested. Much of the country voted Labour because it wanted the Conservatives out. It was a rejection of Toryism rather than an embrace of Starmerism.

And Labour only won 33.7% of the vote but given the vagaries of the first-past-the-post system this was enough to give Labour a large parliamentary majority. This was the lowest proportion of the popular vote that any party that won a majority of seats had ever won in British electoral history, showing that Labour’s grip was much more brittle than its number of parliamentary seats reflected.

Once in office, Starmer’s government failed to produce visible improvements quickly enough. Economically ruinous climate and net-zero policies continued to be pursued. Regulatory overreach strangled innovation and investment. A mad tax regime hounded out capital. Public services are visibly failing across the country. The economy remained a standout laggard among advanced economies. Households remained under great financial pressure. Many young professionals remain unable to afford housing in the places they want to live. The mood of the country is not positive.

That is the challenge Burnham will now face if he becomes, as is likely, prime minister. But the evidence to date around his track record is the that the national mood around him will sour quickly too.

Labour’s national executive committee is expected to open leadership nominations early next month. Because Labour remains the governing party, the winner of the Labour leadership contest will very likely become prime minister.

Burnham has already launched his candidacy. Major potential rivals, including Wes Streeting, have stood aside or moved to support him. Some backbenchers may still try to mount a challenge, if only to avoid a coronation, but the momentum is clearly with Burnham. He should enter 10 Downing Street by mid-July.

Burnham presents himself as a regional champion against the centralising habits of Westminster, arguing that Britain has been governed too long by distant elites who do not understand how the country actually lives. But his programme, likely more interventionist and leftist in key respects even than Starmer’s, is unlikely to inject new momentum in the economy. He wants stronger public control, and in some cases public ownership, over failing utilities such as water and energy. He supports a major social and council house-building programme. He has argued for council tax reform and a more progressive annual property tax aimed at wealthier homeowners. He wants the national £2 bus fare cap restored and favours heavier funding for local social care and mental health services.

Nationalisation, property tax reform, and large-scale social spending all require money. The concern is that Burnham would fund a new age of state activism through higher borrowing, higher taxation, or both. Business interests and fiscal conservatives will warn that such a programme could unsettle markets, deter investment, and return Britain to a model of government that promises control but produces stagnation.

The polling shows that likely consequences of that will be a further fragmentation of British politics. The country no longer organises around its old two-party, Labour-vs-Conservative structure. Mid-June 2026 polling placed Reform UK on 24.0%, Labour on 19.0%, the Conservatives on 19.0%, the Green Party on 15.0%, and the Liberal Democrats on 13.0%.

Britain is not moving from Conservative to Labour, or from Labour to Conservative. It is fragmenting away from both. The old governing parties are being pulled apart from different directions. Reform is attacking from the right. The Greens are attracting disillusioned progressives from the left. The Liberal Democrats remain a confused refuge for anti-Tory and anti-Labour voters in certain parts of the country. The Conservatives and Labour now compete as damaged and often equally directionless brands.

British politics is entering a more volatile age shaped by frustration, fragmentation, and a search for someone who can make the country and the economy work again. It is unclear whether any of the major parties have the answers and ability to meet that demand.