The Government have commissioned an independent review into HS2 will analyse whether and how the project should continue.
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 Department for Transport.
The review's terms of reference state that it will consider how much "realistic potential" there is for cost reductions by amending the scope of the project, such as:
- Reducing the speed of the trains
- Making Old Oak Common the London terminus "at least for a period", instead of Euston
- Building only Phase 1, between London and Birmingham
- Altering plans for Phase 2b, which currently involves taking the line to Manchester and Leeds.