Nigel Farage’s insurgent anti-immigration party, Reform U.K., scored a significant, if razor-thin, victory Friday in a parliamentary special election in the northwest of England, serving notice that Mr. Farage, a populist fixture and close ally of President Trump, is again a rising force in British politics.
Reform’s candidate, Sarah Pochin, won by just six votes over her Labour Party opponent, Karen Shore, in Runcorn and Helsby, seizing what had been a safe seat for Labour until the incumbent, Mike Amesbury, was forced to resign after being convicted of assault for punching one of his constituents.
On a night of high drama, the outcome — the tightest in such an election in modern history — was so close that the vote had to be recounted, delaying the declaration of the result for hours.
But the victory, by 12,645 votes to 12,639, was the start of what could be an impressive show of strength by Reform in mayoral and local council elections held Thursday across England.
More than 1,600 municipal seats are up for grabs, and polls suggest that Reform could win at least 300 of them.
If Reform’s gains are borne out as the ballots are counted throughout Friday, it would deliver a significant jolt to British politics, potentially accelerating the country’s shift toward a more polarized, multiparty system.
For Prime Minister Keir Starmer, it would be a setback in his party’s first electoral test since Labour swept to power in July. The Conservatives, still licking their wounds after last summer’s stinging defeat, would find themselves even more vulnerable to a threat from Reform. And Mr. Farage could make a plausible case that Reform is emerging as a genuine rival to both major parties.
By itself, the Runcorn defeat is a blow to Mr. Starmer. Labour won the seat in the last election with a margin of 15,400 votes. But Mr. Amesbury’s conviction, on top of broader frustration from voters with the government, gave Reform an opening. Ms. Pochin, a businesswoman who served in local government, will join Mr. Farage as one of five Reform lawmakers with seats in Parliament.
Her single-digit victory margin in a special election was without precedent in modern British political history. The closest margin until now was in Berwick-upon-Tweed in 1973, when the Liberal Democrats won by 57 votes.
“The people of Runcorn and Helsby have spoken,” Ms. Pochin said after the victory. “Enough is enough. Enough Tory failure. Enough Labour lies.” She was joined by Mr. Farage, who told reporters that “it’s a huge night for Reform,” and added “we are now the opposition party to this Labour government.”
Peter Kyle, a Labour cabinet minister, told the BBC that the result was “frustrating.” The circumstances of Mr. Amesbury’s resignation had made it a difficult election, he said, but he added that he understood “why a message like this would want to be sent.”
On Thursday in Runcorn, an industrial town of 61,000 that hunkers on the River Mersey, west of Liverpool, the portents of a Reform victory were in the air. People on the main street said the party had capitalized on anti-incumbent fervor, fueled by dissatisfaction with the economy, as well as on tensions over immigration, to win support among voters with deep Labour roots.
In recent years, immigration has become a fraught issue after a local hotel was converted to house migrants, some of whom cross the English Channel in small boats, seeking asylum.
While the Labour government has announced plans to close the hotel, Reform kept a spotlight on it and tried to claim credit for pressuring the government to act.
Terry Osborne, 49, a business development manager, said Reform had tried to exploit the fact that some voters were not aware of the government’s role, and was playing to their pre-existing biases on immigration. “They’ll hear what they want to hear about immigration,” he said.
Mohamed Alosta, 36, a business owner who described himself as a longtime Labour supporter, also criticized Reform’s handling of the hotel issue.
But he said he would not vote for Labour this time because he was disenchanted by the politics of the major parties. Instead, he planned to vote for the Workers Party, a fringe party led by the left-wing firebrand, George Galloway.
In addition to the special election, voters were electing council members in 24 municipalities in parts of England, as well as six regional mayors: in Cambridgeshire and Peterborough; Doncaster; North Tyneside; the West of England; Hull and East Yorkshire; and Greater Lincolnshire.
In the first of the mayoral results, Labour won in North Tyneside, the West of England and Doncaster, with Reform performing strongly and coming second in all three regions. In Greater Lincolnshire, Reform’s candidate, Andrea Jenkyns, a former Conservative lawmaker, was victorious, winning 42 percent of the vote.
Much of what these local officials do is in mundane work like overseeing trash collection or planning. But the elections function as a referendum on the governing party, which racked up a whopping parliamentary majority last year but did so with a thin 34 percent of the national vote.
Since then, Labour’s shallow support has been sapped by unpopular economic decisions like curbing payments to retirees that had helped them cope with fuel costs, hiking payroll taxes on businesses and changing inheritance tax rules for farmers.
“They almost appear to have set out to offend every group,” said Robert Hayward, a Conservative member of the House of Lords and polling expert.
With the next general election years away, there is no threat to Mr. Starmer’s position. But a bad result could increase pressure on the architect of Labour’s austere economic policies, Rachel Reeves, the chancellor of the Exchequer.
Labour’s struggles are not translating into dividends for the Conservatives. The party is bracing for a major loss of seats because the last time this set of local council seats was contested, in 2021, it did unusually well. Voters rewarded Boris Johnson, who was then prime minister, for a speedy rollout of coronavirus vaccines.
