Tory leadership contenders have been warned that opposing the HS2 line will destroy the party’s prospects in key seats for decades, amid concerns that the project will be targeted in the race to replace Theresa May.

Senior figures inside Whitehall, industry and across local government are worried that leading candidates could back either scrapping or seriously scaling back the £56bn scheme in an attempt to win support from wary Tory MPs and fund campaign pledges.

Boris Johnson, one of the favourites to replace May, has raised doubts about the costs of the project. Sources close to Dominic Raab, another leading candidate, said he would look at “getting value for money” for the taxpayer. One cabinet minister, Andrea Leadsom, is opposed to the line, while the Treasury minister and leadership outsider Liz Truss has suggested the project is being reviewed. Michael Gove is known to have been sceptical about the project for some time and is understood to have discussed the idea with MPs in the past.

“HS2 now looks like it could be in trouble, and a lot of money and jobs are connected to it,” one senior Whitehall source said. “But candidates should see this in the context of all the costs. It is a lot of money, but over a long period and part of a wider spending review that will be huge.”

Henri Murison, director of the Northern Powerhouse Partnership, formed to provide a voice for the region’s businesses and civic leaders, said that a betrayal of the project could leave the Tories “in opposition for decades”.

“The leadership election, which can be chaotic and disparate, is encouraging people to go to the lowest common denominator,” he said. “I would predict that cancelling HS2 would send a very negative message to some of those communities and they would be punished at the ballot box.

“It could finish the Tory party in the north of England for a very long time.”

A field near Blackwell, Derbyshire, on the route of the proposed HS2 spur link into Sheffield city centre. Photograph: Christopher Thomond/The Observer

Sir John Peace, the former chairman of British fashion brand Burberry, who leads the Midlands Engine, an organisation designed to boost the region’s economy, said that Britain had underinvested in its infrastructure for decades under successive governments.

“It sounds to me like party leadership electioneering rather than necessarily what is for the good of the country,” he said, adding that HS2 was championed by both main parties, so why was it being questioned now.

Judith Blake, leader of Leeds city council, warned that there would be big costs associated with any changes to the line. “I can’t believe the number of Conservative members sitting in marginal seats in the north will be enthused by that approach,” she said. “This is the opportunity to transform the prospects for the north – perhaps a once in 200-year opportunity.”

Paul Faulkner, chief executive of Greater Birmingham Chambers of Commerce, said: “I think it would be appalling if this were used as a political football in such a way. It is a key piece of national infrastructure at a time when we need to be showing something positive to the world.”

Scott Knowles, chief executive of East Midlands Chamber, said slashing the scheme would “consign the east Midlands to use what is effectively a Victorian railway system”.

Charlie Cornish, chief executive of Manchester Airports Group, called for building work for the line to start in Manchester at the same time as London, “which would help close the north-south divide and help boost productivity in the UK”.

Scrapping the scheme is far from straightforward. More than 900 properties worth almost £600m have been bought up to make way for the route. “In practice, scrapping it probably just means cancelling the section north of Birmingham, which is where the main benefits are,” said one figure close to a leading leadership candidate. “At the moment there is a lot of noise – but let’s see what actually happens.”