Video report by ITV News Wales and West of England Correspondent Rupert Evelyn
An independent review into "whether and how" to proceed with the High Speed 2 (HS2) rail project, has been announced by the Department for Transport (DfT).
"Just because you've spent a lot of money on something should not mean that you should just carry on ploughing more and more money into it," said transport secretary Grant Shapps.
He added: "This is a genuine review to see whether we're going to get the benefits from it, what the full costs are going to be from this project, because its so much money - public money - involved.
"The responsible thing to do is to really look at it and say 'is this actually going to stack up, does it work for the country?'."
The DfT said the review will consider a number of factors relating to HS2, including its benefits, impacts, affordability, efficiency, deliverability, scope and phasing.
HS2 is planned to run up to at a top speed of 225mph – faster than France’s high speed TGV service which currently runs at around 200mph.It will make transport in between some of the UK's commonly travelled to cities and towns much faster.
For example London to Birmingham will take around 49 minutes instead of the 1 hour 21 it currently takes.
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.
Unconvinced homeowners in Yorkshire have also questioned of the value of the public paying to demolish their homes.
Resident Karen Schofield told ITV News: "If there is all this money available let's put it into the health service, better education, better housing, where it is needed.
"Use it where it is needed, do the right thing Boris and axe it."
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."
Watch a visualisation of the proposed HS2 connection between London, Birmingham, Leeds and Manchester:
Mr Shapps said: "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."
Mr Oakervee said: "The Prime Minister has asked me to lead this important review into the HS2 programme.
"I am looking forward to working with my deputy, Lord Berkeley, to advise the Government on how and whether to progress with HS2, based on all existing evidence."
The review's terms of reference state 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
Combining Phase 2a - extending the line to Crewe - with Phase 1
Altering plans for Phase 2b, which currently involves taking the line to Manchester and Leeds
Former Labour transport secretary Lord Adonis claimed the review was "about as stupid as you can get" as it "screws Birmingham and the North".
Writing on Twitter, he added: "Classic Johnson. It throws project into flux and will cause big delays, loss of confidence and cost increases.
"But HS2 will almost certainly continue afterwards in modified form. What a shambles."
However Andy Street, the mayor of the West Midlands who will be on the review panel, said he is "confident" he can "make the business case for HS2 again and win the argument".
He said: "HS2 is mission critical for the West Midlands as it will free up the capacity we so desperately need on our existing railways, drive huge economic growth, and is already creating jobs and building new homes in the region."
ITV News Political Correspondent Daniel Hewitt gives his analysis of the HS2 review:
As Daniel Hewitt says, Prime Minister Johnson made no secrets during the Tory leadership campaign that he had serious reservations about HS2.
Not only did he talk about the spiraling costs and the weak business case but many of his supporters in many Tory shires dislike the project.
Since becoming PM Mr Johnson has shown much more enthusiasm for HS3 - or Northern Powerhouse Rail - a high-speed rail link in the north of England, east to west from Hull to Liverpool.
But a point that will be made by leaders in the north of England is that to have HS3, you have to have HS2.
You have to have the infrastructure in place to build a high-speed rail line from east to west - that's a point they will make to this enquiry.
Daniel Hewitt claims Mr Johnson has to be careful by reviewing HS2.
"There are many, many projects taking place in London," Daniel says, "Is he really going to go toe-to-toe with leaders in the north of England who desperately want this project?"