Boris Johnson has been urged to “change course” on High Speed 2 by more than 20 of his own MPs, weeks after he admitted the controversial project could end up costing the taxpayer more than £100bn.

The newly re-formed HS2 Review Group – which consists of veteran and recently elected Tories, some seated in Labour’s “red wall” – wrote to the PM on Saturday requesting meetings with him and the transport secretary “as a matter of urgency”.

They warned the business case for the project was collapsing, voicing “significant concerns” about government-owned HS2 Ltd’s ability to manage the project and unease over its environmental impact.

“It is not too late for the government to change course,” Banbury MP Victoria Prentis wrote in the letter signed by 20 other Tories. “We have many new colleagues who have campaigned against or are seriously concerned about the future of this project.

“Our fear is that if this project goes ahead as planned, costs will continue to spiral, and the business case will further collapse. We are concerned that not only money but also energy and expertise will be consumed by this project, affecting our ability to deliver on other national priorities.”

Government promises a top-up for HS2 compensation payouts Show all 2 1 /2 Government promises a top-up for HS2 compensation payouts Government promises a top-up for HS2 compensation payouts 43-Train.jpg Government promises a top-up for HS2 compensation payouts hs2.jpg PA

Mr Johnson postponed making a decision on whether to proceed with the project and delayed publication of an official review into it until after the general election campaign, when he admitted the project would probably cost “north of £100bn” – more than double the expenditure proposed initially.

The MPs also voiced fears that the review’s chair, Douglas Oakervee, “is perceived to be in favour of the project because of his previous role at HS2”.

“Indeed, we understand his remit prevented sufficient consideration of alternatives and the panel was not given enough time to do the comprehensive review that this project demands,” they said.

A purported leaked draft of the review – ordered by the PM in summer – was published before the election by The Times, and recommended the project go ahead with minor alterations. However, it also criticised spiralling costs and slipping deadlines.

In their letter, the concerned Tories also reminded Mr Johnson of the need to “restore public trust”, and to “secure the trust” voters in northern constituencies had placed in them.

“As One Nation Conservatives, we need to restore public trust in the process of government and the way we spend taxpayers’ money,” the letter said.​ “HS2 is widely seen as a project that is beset by problems, consistently running over time and over budget.

“The business case is increasingly weakened. We have a duty to ensure that our new northern constituencies benefit from infrastructure investment to secure the trust they have placed in us.”

They requested a meeting with transport secretary Grant Shapps on the morning of 7 January – the day that parliament reconvenes.