Shapps confirmed in a parliamentary statement that Cook estimates that the project requires a budget - including contingency - of £72-78bn at 2015 prices. Shapps says that while the use of 2015 prices provides stability for comparison purposes, it risks being misconstrued. Instead he says the expected cost of the project is equivalent to £81-88bn at 2019 prices against a budget equivalent to £62.4bn.

Regarding the schedule, Shapps says Cook recommends 2028-2031 for the start of operation on Phase 1, with a staged opening beginning with initial services between London Old Oak Common and Birmingham Curzon Street, followed by services to and from London Euston. Cook expects Phase 2b, the extensions to Leeds and Manchester, to open between 2035 and 2040. He also suggested that Phase 2A, the link from the West Midlands to Crewe, could be delivered to the same timetable as Phase 1.

In addition, Shapps reports that Cook believes the benefits of the current scheme are substantially undervalued.

Shapps’ announcement comes amidst an ongoing review into the project, which was confirmed on August 21. Shapps says the review will consider the affordability, deliverability, benefits, scopes and phasing of the project, including its relationship with Northern Powerhouse Rail.

“HS2 is the single largest project of this government,” Shapps writes. “One important aspect of the panel’s work is to consider whether both the costs, and the benefits, of the scheme have been correctly identified. HS2’s business case has been founded on increasing capacity on our constrained rail network, improving connectivity, and stimulating economic growth and regeneration. I want the House to have the full picture. There is no future in obscuring the true costs of a large infrastructure project - as well as the potential benefits.”

The review is set to announce its findings in the autumn, at which point Shapps says he will discuss the findings with the prime minister and chancellor of the exchequer. “Its recommendations will inform our decisions on our next steps,” he says.

Shapps adds that while the review takes place, he has authorised HS2 to continue work on the project. “This will ensure we are ready to proceed without further delay for the main construction stage of Phase 1 in the event that the government chooses to continue,” he says. “Similarly, I intend to continue to progress the next stages of the hybrid Bill for Phase 2a, West Midlands to Crewe, in the House of Lords while the review is ongoing.”

The review is chaired by Mr Doug Oakervee, the former chair of HS2, with Lord Berkeley as deputy chair. The review also includes a panel consisting of Ms Michele Dix, Mr Stephen Glaister, Mr Patrick Harley, Sir Peter Hendy, Mr Andrew Sentance, Mr Andy Street, Mr John Cridland and Mr Tony Travers. Each member will focus on a specific area of expertise, and will feed into the report’s conclusions.