Abandoning high-speed rail in the north of England would be an “appalling dereliction of responsibility” risking tens of thousands of jobs and “the final nail in the coffin” for levelling up, political and business leaders have warned. Rishi Sunak is considering scrapping the Birmingham to Manchester leg of HS2 despite a furious response from senior Conservatives and business chiefs. The move, expected to be announced in the autumn statement in November, would scupper plans for a Northern Powerhouse Rail (NPR), connecting the north of England from Liverpool to Hull, which relies on part of HS2’s network. Amid increasing cross-party anger ahead of the Conservative party conference in Manchester this weekend, the Guardian spoke to more than a dozen northern political and business leaders, who warned: Axing NPR would “throttle” post-Brexit trading initiatives such as Liverpool’s newly opened freeport, which Sunak previously described as vital to “turbo charge” growth; Manchester and Leeds will have lost out on billions of pounds of investment due to prime city centre land that has lain dormant since being ringfenced for HS2 nearly a decade ago; Any cuts to HS2 would “choke off” Birmingham’s recovery from bankruptcy and would make “a complete mockery” of levelling up. Ministers have refused repeatedly to commit to building HS2 in full since Sunak and the chancellor, Jeremy Hunt, met this month to discuss further major cuts to the multibillion pound scheme. The cost of the programme, thought to be the biggest infrastructure project in Europe, is believed to have roughly tripled to about £91bn since it was originally devised in 2009. The project has been beset with delays and mismanagement but remains the biggest regeneration effort in the UK in decades, backed by successive governments going back to when Gordon Brown was prime minister. Henrietta Brealey, the chief executive of Greater Birmingham Chambers of Commerce, said on Wednesday that curtailing the project would put at risk 400 businesses and 8,000 jobs already working on HS2 across the region. “It would be a colossal waste of money, undermine investor confidence and tear up transport and regeneration plans that have been years in the making and in many cases, are mid-delivery,” she said. A letter sent to Sunak by leading West Midlands businesses, including Birmingham airport, said cutting HS2 would be an “appalling dereliction of responsibility”. The Northern Powerhouse Partnership, led by George Osborne and the former Treasury minister Jim O’Neill, said major investment decisions had been made on the basis of HS2 and NPR and that the uncertainty was “wreaking huge damage on business confidence and inward investment”. John Cotton, the Labour leader of Birmingham city council, which declared itself effectively bankrupt this month, said the delivery of HS2 in full was “a vital part of the city’s recovery”. Any cutback would “choke off” Birmingham’s future prospects, he said. Steve Rotheram, the mayor of Liverpool city region, said shrinking the project would cost the area “tens of billions of pounds” in lost investment. His officials had calculated in a business plan that both HS2 and NPR would deliver £15bn of economic growth and about 24,000 jobs for the region. It would also kill a key selling point for the new Liverpool freeport, which opened in January and is one of the government’s flagship post-Brexit trading schemes, he said. He added: “It would leave the north totally moribund and left behind. We would see economic growth happening all around but not here.” Business and political leaders in Manchester and Leeds said huge plots of valuable land had been ringfenced for HS2 for nearly a decade and abandoning the line’s northern leg would mean billion of pounds in lost investment. In Leeds, land worth about £5.6bn had not been developed because it had been “safeguarded” as the site of a new HS2 station since 2013. Bev Craig, the leader of Manchester city council, said: “It’s the final nail in the coffin for levelling up if they scrap or significantly delay the programme. “There’s nothing else going through parliament, there’s nothing else on the books, that meaningfully allocates resource to the north in the way that this does. If they scrap this, it’s effectively the end of any claims of levelling up.” Transport for the North, the statutory body set up by government, passed a motion on Wednesday calling on the government to deliver HS2 and NPR in full. Louise Gittins, the leader of Cheshire West and Chester council, told the meeting that the new rail lines would generate £2bn a year in revenue and 27,000 new jobs in Cheshire and Warrington. She was “horrified” by the prospect of this being lost, Gittins said. The cabinet minister Lucy Frazer said on Wednesday that the prime minister and chancellor would “listen to a wide variety of voices”, but that it was “the responsibility of the government to keep all projects under consideration”. The chancellor is “looking at a whole range of projects to make sure that they are value for money”, she added.