The Government has robustly defended the case for a High Speed rail line despite the publication of a new report suggesting the estimated economic benefits had reduced.
The expected benefit-cost ratio of the HS2 was revised down in the report by the scheme's promoters.
However, the Transport Secretary said the controversial scheme would become the new "backbone of Britain".
Shadow Chancellor Ed Balls has urged the Government to "get a grip" on the costs of the HS2 rail scheme to ensure the project was value for money.
Mr Balls stressed that Labour had supported HS2 "in the past", but said it was vital that costs "stacked up".
An official report released today revealed that the estimated economic benefits of the £50 billion project are dwindling.
Mr Balls said: "We have supported HS2 and there is a case for new investment in a new North-South rail link. But when you have got a project of this scale - £50 billion potentially - you have got to know that it is really value for money.
"In the last couple of years the Government has been all over the place and the costs have got out of control. So my message to David Cameron and George Osborne is 'Get a grip - you shouldn't be cheerleaders, you should be taking a hard-headed look at costs and benefits'."
Transport Secretary Patrick McLoughlin has backed the controversial HS2 scheme, insisting it will become the new "backbone of Britain".
Opponents of the scheme, who believe the project is a waste of money and should be scrapped, seized on an official report published today which revealed that the estimated economic benefits of the £50 billion project are falling.
However, Mr McLoughlin argued the line was not "some expensive add-on" but a scheme which would help people with their daily lives.
Speaking at the National Rail Conference in Manchester, the MP said:
"As the impact of this week’s storm in the south shows, when trains are crowded and disrupted, life for hardworking people gets more difficult. That’s why the new north-south line isn’t some expensive add on. It’s about helping people with their daily lives.
"It’s needed to help commuters who now have to stand - and will soon have to queue - to get on their trains. It’s needed to help the cities of the north which want to compete on equal terms with London. It will be the new backbone of Britain."
Robert Oxley, campaign manager for the Taxpayers' Alliance, believes the Government is "cherry-picking" its figures for HS2 and is creating a "fake boogeyman" by claiming that the alternative - upgrading the current network - would mean years of disruption.
The expected benefit-cost ratio of the HS2 has been revised down in the Government's latest report, falling from £2.50 benefit for every pound spent to £2.30.
It attributed the revision to a £10 billion increase in the scheme's projected £42.6 billion cost, which was made earlier this year.
Transport Secretary Patrick McLoughlin said the current weekend disruption on rail networks shows why upgrading the current rail system is not a viable alternative to the HS2.
He told ITV Daybreak the delays and disruption that occurred during the £9 billion upgrade to the West Coast Main Line proves why a new system is preferable to trying to increase capacity on the current network.
Shadow transport secretary Mary Creagh reiterated Labour's position that there can be "no blank cheque" for the HS2 rail project.
Ms Creagh said:
We must address the capacity problems that mean thousands of commuters face cramped, miserable journeys into cities like Birmingham, Manchester, Leeds and London.
But there can be no blank cheque and ministers must get a grip on costs.
Transport Secretary Patrick McLoughlin is expected to say that although he respects the "lively debate" on the HS2 rail project, it must be a national project with broad support across the political parties "or in the end it will be nothing."
In a speech at a rail conference in Manchester, Mr McLoughlin will tell delegates: "Let me say something very direct to those in the opposition who have learnt nothing from the past.
"You can't say one day you back better infrastructure only the next threaten to stop it being built.
"You can't go on claiming to want one nation if you won't back the things that will bring it together."
The Government is due to publish a report, prepared by Network Rail and management consultancy Atkins, setting out the case for the HS2 high-speed rail project.
This is believed to have concluded that there would have to be 2,770 weekend closures - totalling 144,000 hours of work - on the East Coast, West Coast and Midland main lines if it was to replace the intended capacity of HS2.
The study warns that, during a typical weekend, the journey time from London to Leeds could more than double from two hours 10 minutes to more than four-and-a-half hours.