LONDON — British Prime Minister Keir Starmer had a narrow escape this month, when tremors from the Jeffrey Epstein files shook his leadership and threatened to bring him down.

He faces new danger this week from a special election Thursday in northwest England, where his center-left Labour Party could face defeat by either the hard-line anti-immigration party Reform UK or the self-styled “eco-populist” Green Party. Losing to either would drive home to Labour members how unpopular the prime minister is with voters on both left and right.

The election is in Gorton and Denton, a seat in Greater Manchester that has been Labour turf for a century. Yet Labour’s fortunes have fallen so far that University of Manchester political science professor Rob Ford says victory for Starmer’s party when results are announced early Friday would be considered a surprise “man-bites-dog” outcome.

Local polling and betting markets suggest a close three-way contest between Labour local councilor Angeliki Stogia, Reform UK contender Matthew Goodwin an academic-turned-pundit, and the Greens’ Hannah Spencer, a plumber.

The anti-immigration Reform UK, led by the veteran hard-right politician Nigel Farage, holds just eight of the 650 seats in the House of Commons — Labour has 404 — but has topped national opinion polls for months, ahead of both Labour and the main opposition Conservative Party.

The Green Party has just four seats, but under energetic leader Zack Polanski has expanded beyond environmental concerns to focus on issues including support for the Palestinian cause and the legalization of drugs.

The election’s outcome is hard to call, in a diverse area that has traditional working-class neighborhoods — once strongly Labour, now tilting toward Reform — as well as large numbers of university students and Muslim residents. Many of them feel disillusioned by Labour’s centrist shift under Starmer and the government’s perceived slowness at criticizing Israel’s conduct of the war against Hamas in Gaza.

That makes it fertile ground for the Green Party. Spencer said a win for the Greens would “send shock waves through the political establishment.”

Starmer on Wednesday railed against Green drug policies and urged voters to back Labour to counter Reform’s “hate and division.”

In part, the contest echoes the challenge from populist upstarts faced by mainstream parties around the world.

But some of Starmer’s problems are of his own making.

The British leader has endured a string of setbacks since he led Labour to a landslide election victory in July 2024. He has struggled to deliver promised economic growth, repair tattered public services and ease the cost of living. He pledged a return to honest government after 14 years of Conservative government that ended in scandals and chaos, but has been beset by missteps and U-turns over welfare cuts and other unpopular policies.

The lackluster performance sparked discontent among Labour lawmakers that was ignited into crisis by revelations about former U.K. ambassador to Washington Peter Mandelson in a trove of Jeffrey Epstein files released by authorities in the United States last month.

Police are investigating emails suggesting Mandelson passed sensitive government information to Epstein a decade and a half ago. Mandelson was arrested and questioned by detectives this week before being released on bail. He does not face any allegations of sexual misconduct.

Starmer fired Mandelson in September 2025 after evidence emerged that the ambassador had maintained a friendship with Epstein after the financier’s 2008 conviction for sex offenses involving a minor.

The recent revelations reignited Labour lawmakers’ anger at Starmer’s poor judgment in appointing Mandelson to the Washington job, and pushed some to call for his resignation. After the leader of the Labour Party in Scotland joined those calls earlier this month, Starmer’s chief of staff and communications director quit, and his premiership teetered on the brink.

Starmer vowed to fight on, and got a reprieve after potential leadership rivals publicly backed him. But his position remains precarious.

If Labour loses on Thursday, Starmer will face questions about why the party blocked Andy Burnham, the popular Labour mayor of Greater Manchester, from running. Burnham is widely seen as a potential leadership rival to Starmer.

A loss also would bolster those who argue that the government’s efforts to win over “Reform-curious” voters with policies aimed at curbing immigration have alienated many liberal Labour voters.

The next national election does not have to be held until 2029, meaning the main threat to Starmer comes from within his own party.

Ford said a narrow Labour victory in Gorton and Denton “will buy him a reprieve,” but Starmer still faces peril after May 7 elections for the Scottish and Welsh parliaments and local councils in England, when Labour is expected to do badly.

“It remains to be seen whether the (special election) result panics them into making a challenge now, or whether they bide their time and make a challenge in May — which is likely to be even more gruesome,” Ford said.