Keir Starmer stunned even some close colleagues earlier this week when he abruptly announced plans to push through a radical overhaul of the way Labour elects its leaders at the party’s conference in Brighton. Leaders of Labour-supporting unions were furious about not being consulted in advance, and some shadow cabinet members appeared bemused by the timing of the risky move, just as the government was gripped by a looming winter crisis. Starmer had repeatedly insisted he wanted Labour to look outwards, not inwards – after the Hartlepool byelection defeat in May, he said the party spent too much time “talking to ourselves”. Yet this week’s conference kicked off with fraught negotiations over how his successor will be chosen. Starmer was sent packing from a meeting with trade unions on Friday without their support for the plans, then was forced to make a late-night U-turn and abandon his preferred proposal of a return to an electoral college. But after hours of negotiations, a reform package was agreed on Saturday that the majority of NEC members could sign up to – one that included the requirement for future leadership candidates to gain the support of 20% of MPs, up from 10% under current rules. The phenomenon of a wave of new joiners swaying the result, like the “three quidders” who flooded into the Labour party to back Jeremy Corbyn in 2015, will also be prevented: members will have to have joined the party at least six months earlier to take part. It will also be made harder to force sitting MPs to face a reselection battle, with the support of 50% of members and affiliates now needed to launch the process. Many around Starmer see this as the most crucial win from the package, despite most of the headlines being around the leadership changes. They argue it will prevent MPs spending months in the run-up to the next general election fending off resistance from their own constituency parties. One supportive shadow cabinet member suggested Labour could now have 10 more MPs, had they not been distracted through 2019 by reselection battles. The reform package was voted through on Sunday afternoon after a sustained lobbying effort from frontbenchers, including on the conference floor, and Starmer’s supporters now feel the high-stakes gamble with his own party has paid off. Despite the embarrassment of ditching the electoral college, the proposals have delighted the party’s ardent centrists, who have spent much of the past five years weighing up how best to prevent a political outlier like Corbyn from ever winning again. Deeply scarred by that period, which culminated in a damning report about the handling of antisemitism complaints by the Equality and Human Rights Commission and the worst electoral loss since 1935, they see it as essential to raise the hurdles for future candidates to jump. A spokesperson for Starmer said the package would “better connect us with working people and reorient us toward the voters who can take us to power”. In pressing the reforms, however, Starmer appears to have decisively ended any lingering sense that he would seek to act as a bridge between Labour’s warring factions. Instead, he appears determined to take on and defeat the Corbynite left. Some senior party figures blame a small group of advisers around him, obsessed with preventing the party falling into the hands of a leftwinger. But backers of the plans argue they will help get Labour in fighting form for the next general election, leaving next year’s conference free to set out the stall for a potential 2023 general election. One veteran of the battles during the Corbyn era said Starmer had “done his duty by the institution” of the Labour party. But in doing so, he has set one wing of the party against another once again. NEC members from rival camps were sparring openly on Twitter on Saturday after the reforms were discussed. During his leadership campaign, Starmer was able to use the issue of Brexit to cut across Labour’s great left-right rift, winning over many former Corbyn fans in the process. But in Brighton this weekend, the party’s deep divisions were on clear display.