The governing Conservative Party was long seen as entrepreneurs’ natural ally and lobbyists’ most important target. With an election on the horizon, that’s changing.It was impossible to miss: a large green, yellow and blue off-road vehicle parked in a prime spot in the exhibition hall at the Labour Party’s annual conference. The car belonged to Ineos, one of the world’s largest chemical companies, and its outsize presence, among dozens of businesses and organizations, marked the company’s first time attending the gathering.Andrew Gardner, who runs Ineos’s huge refinery complex in Grangemouth, Scotland, was standing by the vehicle on Tuesday afternoon, grabbing time with passing Labour lawmakers to discuss the company’s goals.He had never attended a Labour conference before, and skipped the governing Conservative Party’s the previous week, but said he had come to this one, in the northern English city of Liverpool, because Labour was expected to form the next government. His colleague Richard Longden, Ineos’s head of communications, chimed in, describing “a vibe here of a party that’s changed, and one that’s looking forward to the future. And business needs to be speaking to them and needs to be seen.”“Which is exactly why we’re here,” Mr. Gardner added.In Britain, the Conservative Party has traditionally been seen as the party of business and the guardians of free enterprise. Now, under the centrist leadership of Keir Starmer, Labour is taking over that mantle. As the party inches closer to power, with a general election expected next year, it is engaged in a mutually beneficial love-in with the corporate sector.At the four-day conference this week, attended by 18,500 people, British executives and lobbyists representing industries from finance and technology to construction and defense crammed into bars, corridors and meeting rooms as Labour made its pitch to be “the undisputed party of business,” in the words of Jonathan Reynolds, a lawmaker who speaks for Labour on the issue.The record attendance was boosted by companies showing up for the first time, decamping from their more familiar habitat of Conservative Party gatherings, including Ineos, whose CEO and founder is the billionaire Brexit supporter Jim Ratcliffe.Ineos’s refinery complex in Grangemouth, Scotland. The company, whose founder is a billionaire Brexit supporter, had a strong presence at Labour’s conference.Andrew Testa for The New York TimesMr. Gardner said that Labour was already saying 80 percent of what he wanted to hear in terms of decarbonizing large-scale industry, as the company invests in reducing its carbon emissions. (That off-road vehicle was hydrogen-powered.) But he was there to push for the last portion, which was to lobby Labour not to end natural gas exploration in the North Sea too soon.That message was “slowly percolating,” he said. And there was some evidence that Ineos was being heard: Rachel Reeves, who would become Britain’s first female chancellor if Labour win next year, mentioned Grangemouth in her speech to party members.The party brought together about 200 executives on Monday at a forum within the conference to meet would-be cabinet ministers.“What we are experiencing is a party who tell us that, if elected, they want to be business-friendly government, that they want to work with the private sector in partnership,” said Chris Hayward, who speaks on policy questions for the City of London, Britain’s historic financial district.At a reception on Tuesday evening held by Labour Business, a forum to engage with the commercial sector, the mood was almost euphoric. As guests sipped wine and ate canapés, the group’s chairman, Hamish Sandison, said that not only had the tide turned in terms of Labour’s relationship with business, it had “become a tsunami.”That enthusiasm partly reflects strained relations with the governing Conservatives, particularly over Britain’s exit from the European Union, which many big corporations opposed.Boris Johnson, a former prime minister, famously dismissed the concerns of businesses over Brexit in crude terms. His short-lived successor, Liz Truss, caused markets chaos with her plans for unfunded tax cuts. And although her successor, Rishi Sunak, restored some calm, he has recently upset many businesses by abruptly changing targets on some net zero plans and canceling part of a high-speed train network.Labour has been on a journey, too. Its previous leader, Jeremy Corbyn, promised nationalization of key industries and big increases in public spending funded by higher taxes. That agenda has been unceremoniously junked by Mr. Starmer, who became leader in 2020 and moved to purge his predecessor.Labour’s shift attracted some surprising names, like JCB Hydrogen, an energy firm, which handed out tote bags to party members. Its chairman, Anthony Bamford, was a prominent supporter of Brexit and, during the last general election in 2019, hosted a campaign event for Mr. Johnson.Outside the Labour conference on Tuesday. It had 18,500 people in attendance.Jon Super/Associated PressWhat draws many businesses to Labour is the prospect of a more stable policy environment, which could be cemented by the party’s plans for a long-term industrial strategy — an idea that runs counter to Mr. Sunak’s free-market instincts.Carl Ennis, the head of Siemens in Britain and Ireland, was also at the Labour conference for the first time. He was there to lobby for an “overarching” and long-term approach, which was something that the Conservatives were struggling to provide, he said. “My job is to make the U.K. an attractive place for Siemens to invest its money in,” he said, adding that Labour’s industrial strategy appealed to him.In every meeting room, businesses had the same central plea: Give us consistency. And the Labour party was receptive, said Shevaun Haviland, the director general of the British Chambers of Commerce. “We feel very positive that the party’s listening to what we have to say and what our members have to say,” she said.Ben Wilson, vice president of public policy for Mastercard, said that his experience of engaging with the party was “indicative of how open Labour is to business,” saying that he and other executives had the opportunity to discuss policies that could form part of the platform of the “next government.”All this has revived memories of the 1990s when, in the years before Tony Blair became prime minister, the party wooed business over lunches and dinners in what was nicknamed the “prawn cocktail offensive.” This time much of the interaction has been over breakfast with Ms. Reeves, nicknamed the “scrambled eggs and smoked salmon offensive.”“Ever since I became shadow chancellor I’ve had this aim to reach out to business,” Ms. Reeves, a former economist at the Bank of England, said at a small event on the sidelines of the conference. “A lot of the businesses that I’ve met over the last two and a half years would have seen, in some of the announcements this week, their fingerprints on our policies.”While some on the left of the party were unnerved by the dominant presence of business and its influence on future policy, other supporters suggested it was the inevitable result of Labour’s double-digit poll lead.“Businesses are here in numbers,” said Stephen Kinsella, a former antitrust lawyer and Labour donor. “There are a lot of people who want to back a winner, think they have spotted a winner and realize they need to get to know the people who are going to be in government.” More