Labour has overturned massive Conservative majorities in a history-making pair of byelections, sending the Tories deeper into in-fighting and acrimony over the prospect of a landslide defeat at the upcoming general election. The wins in Mid Bedfordshire and Tamworth prompted gleeful talk within Labour of a possible 1997-type win on the horizon, but Keir Starmer’s aides were quick to warn MPs and the party more widely against complacency. Making celebratory visits to both seats, Starmer said Labour was “redrawing the political map” in winning both constituencies due to massive swings from the Conservatives. The 23.9-percentage-point switch in Tamworth was the second-biggest Tory-to-Labour shift since 1945, while the Conservatives’ previous 24,664 majority in Mid Bedfordshire was the biggest margin to be hauled back in any recorded UK byelection. While the Labour majorities were relatively small – both little over 1,000 – and delivered as much as anything by Conservative voters staying at home, a double win that exceeded many pre-vote predictions prompted inevitable comparisons with the party’s march towards victory in the run-up to 1997. One senior Labour source said it was “important that people keep their feet on the ground” and not assume all such Tory strongholds were for the taking in a general election. “They need to be conscious of the scale of the challenge – we need a bigger swing than Tony Blair in 1997 just to get a majority of one. Yes, enjoy the results, be proud, but then it’s back to work,” they said. “When you have swings over 20 points it’s going to put a spring into your step, but we want to avoid any sense of complacency.” Starmer was similarly cautious, revelling in the victories and congratulating campaigners but also saying that Labour took the success “humbly”. Speaking next to Alistair Strathern, who also saw off a vigorous Liberal Democrat challenge to succeed Nadine Dorries in Mid Bedfordshire, Starmer said Labour was “redrawing the political map” by taking a seat that had returned Tory MPs in every election since 1931. “We know that voters here have voted for us and they’ve put their trust and their confidence in a changed Labour party, and we will repay them for that trust and confidence,” he told assembled activists. “We do so humbly. And I know there are people yesterday who probably voted Tory in the past who voted for a changed Labour party because they despair at the state of their own party.” In his next engagement, joining the new Tamworth MP, Sarah Edwards, inside the town’s football stadium, Starmer was more ebullient, telling campaigners: “People told me that it was not possible to win this seat and this byelection. You absolutely smashed it.” A source close to Rishi Sunak, who was meeting leaders in the Middle East, said the Conservatives viewed the losses as “disappointing, but not unexpected” given a context including the background to the byelections. Dorries, the former culture secretary, quit her seat after 11 weeks of public disgruntlement about not being made a peer in Boris Johnson’s resignation honours, while the Tamworth byelection was called after Chris Pincher, the former deputy chief whip, faced suspension from parliament for groping two men. “Byelections aren’t about picking a government, they’re about sending a message, and they should be seen in that light,” the Conservative source said. “This does not feel like an endorsement of Keir Starmer.” Speaking to reporters just before he flew back to the UK from Egypt, where he met Mahmoud Abbas, president of the Palestinian Authority, Sunak reiterated this point: “It is important to remember the context – midterm elections are always difficult for incumbent governments. And of course there are also local factors at play here.” Pushing back against any idea of a tactical rethink after the defeats, Sunak stressed his commitment to targets such as halving inflation, and repeated his pledge from this month’s Conservative conference to bring “change” to British politics. While even Sunak’s fiercest opponents on the Tory benches discount the idea of a formal challenge to his leadership, he will face increasing pressure from some MPs to change tack, notably over the idea of tax cuts in next month’s autumn statement, or to push harder on culture war issues. Doing either, however, would risk alientating more centrist Tories, with one backbencher warning against a return to what they called “the Poundland Thatcherism” of Liz Truss. They added: “MPs are obviously jittery. There is no enthusiasm for Labour but also an absence of any apparent strategy from the government. If we get it wrong, we risk turning a challenging situation into a disaster.” Tensions could be further inflamed by the prospect of further tricky byelections, with the veteran MP Peter Bone having lost the Tory whip and facing a possible suspension over a finding that he bullied and harassed a former staff member, which Bone denies. Both byelections saw the Conservative vote collapse, taking the party from a 66% share to 41% in Tamworth and from 60% to 31% in Mid Beds. The Labour vote rose more moderately. John Curtice, a professor of politics at the University of Strathclyde, said the results were “extremely bad news” for the Tories. “If you want to look at the precedent: what’s the last time that we had swings of this order? The answer is the parliament of ’92 to ’97. There were four byelections in that period in which Labour got swings of over 20% from the Conservatives, and we all know how that ended,” he said.