Rishi Sunak is facing open revolt from the top of his party, key advisers and business leaders over HS2 after The Independent’s revelations about plans to ditch the multibillion-pound project.

Two former Tory prime ministers, the government’s infrastructure tsar, northern powerhouse groups and mayors both north and south came out on Saturday to slam Mr Sunak.

Two former Tory prime ministers, the government’s infrastructure tsar, northern powerhouse groups and mayors both north and south came out on Saturday to slam Mr Sunak.

Clamour has been building since The Independent broke the story ten days ago, detailing how sunk costs of £2.3bn could be offset by a £34bn saving if HS2 was scrapped north of Birmingham.

This newspaper outlined how the so-called Project Redwood was drawn up to enable the prime minister and chancellor to sit down face-to-face to discuss the cost benefits.

Despite repeated questioning from the British media, Downing Street has repeatedly refused to say whether the long-running and over-budget scheme will go ahead.

The Independent understands a decision on the project could be announced as early as Friday, ahead of the Tory conference in Manchester, to try and quell discontent.

A chorus of objection to scrapping the second phase of the project came from:

• Sir John Armitt, the government’s infrastructure commission chair, said it would be a “disaster.”

• Boris Johnson called it “Treasury-driven nonsense” which would “mutilate” HS2

• David Cameron is said to be concerned that it would be anti-conservative

• London Mayor Sadiq Khan described ditching the project as a “colossal waste of money.”

• West Yorkshire mayor Tracey Brabin warned the move would damage jobs, investment and economy

• Business group the Northern Powerhouse Partnership said cutting back the line would be “wrongheaded.”

Among the proposals being considered is stopping the line north of Birmingham, while another section of line into central Manchester, also set to be used by the Northern Powerhouse Rail project, is apparently on the chopping block and could be cut to save costs.

The final stretch of the line into Euston, the most expensive part of the project, could be abandoned in favour of terminating at Old Oak Common, six miles north.

Mr Johnson this weekend branded cost-saving measures “desperate”, urging the prime minister to deliver on the 2019 levelling-up pledge the Conservatives were elected on. He said it would “mutilate” the whole project.

“It is the height of insanity to announce all this just before a party conference in Manchester,” he said. “It is no wonder that Chinese universities teach the constant cancellation of UK infrastructure as an example of what is wrong with democracy.”

According to The Times, Mr Cameron has also privately raised significant concerns about the possibility that the high-speed rail line could be heavily altered.

In a letter to Mr Sunak, mayor of London, Mr Khan warned that it would take longer to get from Birmingham to central London on HS2 than existing trains if plans to terminate at Euston station were abandoned.

“The government’s approach to HS2 risks squandering the huge economic opportunity that it presents and turning it instead into a colossal waste of public money,” the Labour mayor said in a letter to the PM.

When the railway first opens between London and Birmingham, expected between 2029 and 2033, its terminus in the capital will be Old Oak Common, in the western suburbs.

Mr Khan said: “Terminating the service at Old Oak Common would be a short-sighted decision which will have long-term implications, significantly downgrading the value of HS2 as a high-speed connection and leaving a ridiculous situation where a ‘high speed’ journey between Birmingham and central London could take as long as the existing route, if not longer.”

He said the “best case” journey time of one hour and 22 minutes from Birmingham to Euston, changing at Old Oak Common onto the Elizabeth line and Northern line, was “already one minute longer than the existing train time”.

Tracy Brabin, mayor of West Yorkshire, added: “Scrapping the project in the north of England will damage jobs, investment and the economy and leave plans to level up in tatters.

“Big infrastructure projects need long-term commitment over successive governments. There must be a better way than this piecemeal stop-start approach that we have seen from this government.”

Henri Murison, chief executive of the Northern Powerhouse Partnership, representing businesses across the north, told The Independent: “For both the north and London, the government is considering wrongheaded choices.”

“As Boris Johnson rightly argues, this isn’t just the worst of Treasury orthodoxy stopping the most vital sections of HS2 allowing the north to benefit, but losing Northern Powerhouse Rail – or the Charles line as leading northern Tory John Stevenson has christened it.

“The current prime minister convinced Boris to make it central to his domestic policy platform and general election campaign. It is time for him to remember it was largely down to him – remember he is a northern parliamentarian and respect the mandate of the 2019 election.”

HS2’s original leg to Leeds via Sheffield was already scrapped under Mr Johnson’s premiership while Mr Sunak was chancellor.

Labour’s official policy is to build HS2 fully, including the previously cancelled spur to Leeds. Though spokespersons for the opposition party have, at times in the past two weeks, appeared reluctant to confirm this.

It is also understood that any move by the government to pull the legislation for the northern phase of the project – which is currently going through parliament – would significantly complicate the process for a new government attempting to complete it.

This week, Mr Hunt said the government was “looking at all the options”, adding: “We do need to find a way of delivering infrastructure projects that don’t cost taxpayers billions and billions of pounds.” The Treasury chief said no decisions had yet been taken.

A government spokesperson said: “The HS2 project is already well underway with spades in the ground, and our focus remains on delivering it.”