The House of Commons Public Accounts Committee has published a report into the planning to date of the High Speed 2 project.
The report – High Speed 2: a review of early programme preparation – says that the case has not yet been made for the need for the new rail line.
“So far the Department has made decisions based on fragile numbers, out-of-date data and assumptions which do not reflect real life,” it says.
It also voices concern that the target of reaching Royal Assent for the enabling legislation by the end of March 2015 is unrealistically tight.
Public Accounts Committee chair Margaret Hodge said: “The Department for Transport has yet to present a convincing strategic case for High Speed 2. It has not yet demonstrated that this is the best way to spend £50 billion on rail investment in these constrained times, and that the improved connectivity will promote growth in the regions rather than sucking even more activity into London.
“The pattern so far has been for costs to spiral - from more than £16 billion to £21 billion plus for phase one – and the estimated benefits to dwindle.
“The Department has been making huge spending decisions on the basis of fragile numbers, out-of-data data and assumptions which do not reflect real life, such as assuming business travellers do not work on trains using modern technology.
“As usual with NAO reports, the Department had agreed the facts in the report as accurate before publication. However, as soon as the report was published, the media reported unnamed departmental sources as claiming that it contained errors and was based on out-of date analysis. These claims were quite unfounded.
“The Department has ambitious and, in our view, unrealistic, plans for passing the Bill for High Speed 2. The timetable is much tighter than for either High Speed 1 or Crossrail, despite the fact High Speed 2 is a much larger programme. In my committee’s experience, not allowing enough time for preparation undermines projects from the start. A rushed approach contributed to the failure of the InterCity West Coast franchise award."
In response the transport secretary Patrick McLoughlin said: "I welcome any examination of HS2, but I do not accept the PAC’s core conclusions. The case for HS2 is absolutely clear: without it, the key rail routes connecting London, the Midlands and the North will be overwhelmed. The project will free up vital space on our railways for passengers and freight, generate hundreds of thousands of jobs and deliver better connections between our towns and cities.
“This government is investing record amounts across our transport network – trebling spending on major road schemes and funding the biggest upgrade to our railway in modern times. HS2 is a vital part of our plan to give Britain the transport infrastructure it needs to compete."