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Tory splits over the HS2 high speed rail link have burst open after a leaked government-commissioned review warned it could cost up to £106bn.

A group of 30 pro-HS2 Tory MPs from the north and Midlands, including senior ministers, have put their name to a private letter to Boris Johnson underlining their support for the project.

It came in response to reports that more than a dozen Tories, including from the new intake who seized so-called “red wall” northern and Midlands seats from Labour, were prepared to meet the prime minister to urge him to cancel HS2.

The split adds to the dilemma Johnson faces as he prioritises infrastructure investment as part of his efforts to close the north-south divide and serve voters who backed the Tories at the election. 

The review led by former HS2 Ltd chairman Doug Oakervee, leaked to the Financial Times, found there is “considerable risk” that the high-speed rail project’s cost will rise by up to 20% from between £81bn and £88bn.

It was initially allocated far less – £56bn – in 2015.

The review also recommended that the second stage of the project, to take the line beyond the initial London-Birmingham link onwards to Manchester and Leeds, should be paused to probe whether it would be better to downgrade it to a mix of high-speed and conventional lines. 

But Kevin Hollinrake, who is organising the pro-HS2 letter alongside Crewe and Nantwich’s new Tory MP Kieran Mullan, told HuffPost UK: “If we have a change of heart now, you are still going to deliver HS2 to Birmingham.

“What’s the rest of the country going to think of that?

“The north is left out again – it would look very bad.”

Hollinrake welcomed the “robust challenge” from Tory colleagues but said they were wrong to portray the decision as an “either/or” choice between HS2 and boosting transport within the north.

The MP for Thirsk and Malton, in North Yorkshire, is a supporter of the proposed northern powerhouse rail (NPR) link between Liverpool, Manchester, Bradford, Leeds and Newcastle. 

But he said: “It is the wrong thing to superconnect the north into one geographic region and then not connect it to the rest of the country.”

Half the infrastructure for NPR will be also be shared with HS2, which will be built first, Hollinrake said.

He is keeping his letter private as a number of ministers have signed it and need their views to be kept private, including “very senior people”.

The MP said he has also had “very positive” conversations about HS2 in the past with “senior treasury ministers”.

His impression is that the government is currently “on the fence”, adding: “I think if you’re on the fence on something like this, at a time like this, I think you should come down on the side of investment.”

On the other side of the Tory party, Dehenna Davison said the project would not give value for money and called for transport between northern towns and cities to be prioritised.

Davison, who in December won Bishop Auckland in County Durham for the Tories for the first time ever, said: “I’m all in favour of investment in infrastructure. 

“However, with the ballooning costs of the HS2 project, I find it difficult to believe it will provide value for money for taxpayers. 

“I also believe that our infrastructure agenda should prioritise the north, and focus on connecting our northern communities, rather than entering around the journey times to London. 

“To guarantee we spread opportunity across the country we must ensure that we have effective transport links to and from our great cities and towns in the north.”

The Oakervee review concluded that the government should “on balance” continue with the 250mph railway but that this was 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.”

Several construction bosses also claimed scrapping the project would cause “irreparable damage” to the industry and suggested it could cost jobs.

The chief executives of Balfour Beatty, Skanska and Morgan Sindall were among the signatories to a letter to Johnson, seen by the Times, which urged him to approve the scheme and noted it would take “many years to get an equivalent pipeline of work in place” if HS2 were cancelled.

A decision on whether to go ahead with the project will be made in “weeks rather than months”, transport secretary Grant Shapps said.

£8bn has already been spent on the project.