Boris Johnson could decide to scrap HS2 by the end of the year after his government announced an immediate review into whether the £55 billion project should go ahead.
The Department for Transport today announced a Government-commissioned independent review into HS2 will analyse whether and how the project should continue.
The first phase of the line is due to open in 2026 linking London and Birmingham. It would then be extended to Manchester and Leeds by 2033.
However, reports have suggested the cost of setting up the 200mph lines could go billions over budget.
Former HS2 Ltd chairman Douglas Oakervee will lead the inquiry, with Lord Berkeley - a long-term critic of the high-speed railway scheme - acting as his deputy.
The DfT said the review will consider a number of factors relating to HS2, including its benefits, impacts, affordability, efficiency, deliverability, scope and phasing.
A final report will be sent to Transport Secretary Grant Shapps - with oversight from Prime Minister Boris Johnson and Chancellor Sajid Javid - by the autumn.
This will "inform the Government's decisions on next steps for the project", according to the DfT.
Mr Shapps said: "The Prime Minister has been clear that transport infrastructure has the potential to drive economic growth, redistribute opportunity and support towns and cities across the UK, but that investments must be subject to continuous assessment of their costs and benefits.
"That's why we are undertaking this independent and rigorous review of HS2.
"Douglas Oakervee and his expert panel will consider all the evidence available, and provide the department with clear advice on the future of the project."
