Keir Starmer has hailed Labour’s “seismic” win in Blackpool South in a night of local elections that provided further evidence that the party is heading for a large majority at this year’s general election. The Labour leader called the result in the Blackpool South byelection “truly historic” after the party’s candidate, Chris Webb, won the seat with the third biggest swing from the Conservatives to Labour in postwar history. Webb, a local and the firm favourite, won with 10,825 votes, followed by David Jones, the Conservative candidate, with a distant 3,218 votes, who finished narrowly ahead of the Reform candidate, Mark Butcher, on 3,101 votes. Webb’s victory is the latest sign that Labour is winning again in leave-voting areas it lost to Boris Johnson’s Conservatives in 2019, with the party also gaining control of the councils in Rushmoor, Thurrock and Hartlepool. However, it was defeated in Oldham, amid signs that it has lost ground in areas with high Muslim votes as a result of the party’s stance on the war in Gaza. Starmer said on Friday morning: “This seismic win in Blackpool South is the most important result today. This is the one contest where voters had the chance to send a message to Rishi Sunak’s Conservatives directly, and that message is an overwhelming vote for change.” Webb’s win in Blackpool South came on the back of a 26 percentage point swing, the third largest from the Tories to Labour since the second world war and the fifth time in the last 18 months it has won a seat from the government on a swing of more than 20 percentage points. John Curtice, professor of politics at Strathclyde University, told the BBC the results were further indication of a significant Labour majority to come at the general election. “This is now the fifth parliamentary by election in which we’ve seen swings of over 20% from Conservative to Labour,” he told Radio 4’s Today programme. “The last time we had swings with that size of a degree of regularity was the 1992-1997 parliament. Tony Blair didn’t get as many as that, and we know what happened in 1997.” Jonathan Carr-West, the chief executive of the Local Government Information Unit, said: “Against the backdrop of a steady Conservative decline since 2019, the results so far indicate the trend will not be bucked this year.” Pollsters said early results suggested the Tories could lose half of the council seats they contested on Thursday night, putting them on course for as many as 500 losses. Bad results are likely to lead to another attempt by Tory rebels to oust the prime minister just months away from the general election. However, Sunak’s allies have pinned their hopes on retaining the mayoralties in the Tees Valley and West Midlands, where polls show the results are likely to be very close. While Labour celebrated its successes in Blackpool, Thurrock and Hartlepool, the party suffered shock losses in Oldham where it surrendered control of the council. Several Labour candidates lost their contest to independents amid deep local unhappiness over Starmer’s stance on Gaza. Carr-West said: “This is the first indication that the party’s position on Gaza may cost it votes in this election and we will be watching how this plays out in other areas. It’s a reminder of how global and local politics intertwine and that local elections are not a straight dress rehearsal for the general election.” Many in the party believe the Labour leader has been slow to criticise Israel’s actions in the Middle East, and insensitive to the anger it has caused among British Muslims and progressive voters. Some believe this could cost the party as many as a dozen potential victories at the general election, although with Labour making such large gains elsewhere, experts say this is unlikely to cost the party a majority. For Sunak’s party, the loss of Blackpool South was not unexpected but may be taken as an indication of how voters in less affluent constituencies are likely to vote in the general election expected later this year. The constituency includes some of the UK’s most deprived wards, where many would argue the government has not delivered on its promises of levelling up. The byelection was triggered after Scott Benton stood down in March over a lobbying scandal. It was discovered in April 2023 he had offered to table parliamentary questions, leak documents and lobby ministers on behalf of gambling companies in return for “thousands of pounds per month”. He sat as an independent MP after being suspended from the Conservative party, and was later suspended from the House of Commons. The Conservative candidate faced competition from Reform’s Butcher, a local businessman who runs a soup kitchen being investigated by the Charity Commission over claims it was used to promote his campaign. Reform ran a strong campaign in which Butcher distanced himself from the wider party, insisting he was “not a politician” and taking aim at the Tories and Labour, which played well in hustings. Reform recently overtook the Lib Dems nationally to take third place in opinion polls and has led an ambitious local election campaign, fielding 300-400 candidates for councils across England. Meanwhile, those same polls show support for Labour has stayed level since dropping back after peaking during the short-lived Liz Truss prime ministership in 2022. “It was a cracking good night,” Gawain Towler, Reform’s spokesperson, told the Guardian. “Of course we would have liked to have done better, we always do, but this is the best we’ve ever done. We’ve shown ourselves to be an effective force and success breeds success.” He said Butcher should be “proud” of achieving such strong results and was now an experienced campaigner with one fight behind him. “You’re gonna be disappointed because that extra 100 votes would have made such a difference but he knows how well he’s done,” Towler said.