HS2 could cost up to £106 billion, according to a widely leaked Government-commissioned review.
An inquiry led by former HS2 Ltd chairman Doug Oakervee reportedly found there is “considerable risk” that the high-speed rail project’s cost will rise by up to 20%.
A report by current HS2 Ltd chairman Allan Cook, published just four months ago, set out an estimated cost range of between £81 billion and £88 billion.
HS2 was allocated £56 billion in 2015.
A decision on whether to go ahead with the project will be made in “weeks rather than months”, Transport Secretary Grant Shapps said.
The review concluded that the Government should “on balance” continue with the 250mph railway, which would initially go from London’s Euston station to Birmingham and then to Leeds and Manchester by 2040, but that this is subject to “a number of qualifications”.
It said “further work” is needed to assess HS2’s impact on regional growth, and warned that it is “hard” to say what economic benefits will result from building it.
“Transport investment alone will not ‘rebalance’ the UK economy,” the review adds.
Greater Manchester Mayor Andy Burnham described the leak as “quite worrying” and claimed that using conventional lines in the North would be a “second-class option”.
He told BBC Breakfast: “It’s the same old story. London and the South gets whatever it wants, and it’s all about penny-pinching in the North.”
Judith Blake, leader of Leeds City Council, said: “It is time to bring the damaging speculation around HS2 to an end with the prompt publication of the Oakervee Review and an unambiguous Government commitment to deliver the project in full.”
The chief executives of Balfour Beatty, Skanska and Morgan Sindall were among the signatories to a letter to Boris Johnson, seen by the Times, which urged him to approve the scheme and noted that it would take “many years to get an equivalent pipeline of work in place” if HS2 was cancelled.
But a group of more than a dozen Tory MPs will reportedly meet the Prime Minister in the coming days to urge him to block HS2 and spend the money on other projects.
Mr Johnson is expected to decide within weeks whether to go ahead with construction on the first phase of what would be Europe’s largest infrastructure project.
The review said savings to the £106 billion figure could be made by having the private sector contribute to funding HS2 stations, lowering specifications and improving the “cost performance of the management”.
It also stated that no other high-speed line in the world runs 18 trains per hour, and recommends reducing HS2’s frequency to 14.
Mr Shapps said the “massive decision” on whether to go ahead with HS2 “needs to be fact-based”.
He told Sky News: “I asked Doug Oakervee to do that report and said to him ‘Give me the facts, give me the data, give us the information so we can make a proper, informed decision’.
“I’ve always approached this from a relatively neutral point of view and that information will help to inform a decision that is best for the whole country.”
£8 billion has already been spent on the project.