The Conservative mayor of the West Midlands has told Boris Johnson cancelling HS2 would fail the new Tory voters who returned him to No 10 last month believing he would bring prosperity to their region.

As the government prepares to publish a review into the future of the high-speed railway line, Andy Street said abandoning the project would deliver a “hammer blow” to the West Midlands from which it could take a decade to recover.

Street was a member of the panel on the Oakervee review into HS2, which has been submitted to Grant Shapps, the transport secretary.

A leaked early draft last year suggested the recommendation would be to press ahead with HS2 with some running costs scaled back. However, the review’s deputy, Lord Berkeley, published his own dissenting assessment last week claiming costs had risen to £108bn – more than double the original estimated amount.

With political pressure on Johnson to reduce spending on the project, Street told the prime minister the railway line was “mission critical” to the West Midlands.

“Since reviewing all the evidence, my position has only hardened – HS2 could make or break the future of the West Midlands,” he said, highlighting the thousands of jobs that had already been created by the project.

“If HS2 does not go ahead, I fear the West Midlands economy will suffer a hammer blow from which it might take decades to recover. Moreover, residents across the region, many of whom voted Conservative in last month’s general election, are all too aware of this.

“The prime minister helped build his 80-seat majority in part thanks to a huge swathe of new voters in the West Midlands. They are now expecting him to deliver on his promise to rebalance the economy and power up our region. The first clear and decisive step that can be taken to fulfil that promise is to back HS2.”

Street acknowledged the government needed to “get a grip of both the costs and timeline” and inject some more “vision”, such as by linking the line to Eurostar, but insisted these issues could be rectified. Failing to press ahead with the project would be a huge missed opportunity, he said.

Douglas Oakervee, a former HS2 chair, was commissioned by the government in August to review the line’s costs, suggest savings and produce a “go or no-go” conclusion. His review suggests running fewer trains an hour but says all sections of the line should be built.

The leaked draft showed Oakervee was endorsing the project, despite revising down the expected economic benefits from £2.30 for every £1 spent to between £1.30 and £1.50 per £1.

However, Berkeley, whose inclusion as deputy review chair was cited by ministers as demonstrating balance, said the draft still overestimated the benefit-to-cost ratio, and predicted HS2 would make a £40bn loss.

Johnson promised a review of HS2 during his leadership campaign. He has previously sounded sceptical about the project and many of the Tory backbenchers who supported him were pushing for it to be abandoned.

However, he is keen on major infrastructure projects that benefit areas outside south-east England. During the election, Johnson told reporters: “You know where my instincts are. I’ve overseen a great number of very big infrastructure projects. I’m going to hesitate before simply scrapping something that has been long planned and is of great national importance.

“But we will want to be checking the money is being properly spent and there aren’t ways in which it could be reprioritised or reprofiled.”