Government insists HS2 still has cross party support

Mr Darling, who as chancellor first approved stages of the line, said the economic benefits of the project are “highly contentious”.

His views add to growing concerns over the project, and its cost. Earlier this week the Institute of Economic Affairs estimated the eventual cost of the scheme could be as high as £80bn.

‘Nightmares’

“It is time to revisit the case for HS2,” Mr Darling said. “It runs the risk of substantially draining the railway of money vital for investment over the next 30 years.

“My experience in government also makes me suspicious of big projects that can easily run out of control.

“Politicians are always excited by ‘visionary’ schemes. One thing I have learnt is that transport, rather like banking, is at its best when it is boring. That is when it tends to work.

“Political visions can easily become nightmares.”

‘Highly contentious’

Mr Darling agreed that there are capacity problems on the route from London to the Midlands – but questioned why new trains needed to be “high speed”.

He said: “Certainly it’s handy to cut the journey time between Birmingham and London by half an hour. But at what cost?

“The economic benefit that is claimed will come from this is highly contentious. The business case depends on an assumption that passengers aren’t productive – that is, that they don’t work on the train.

“That may be true on a commuter train but not on long-haul intercity services. Arguably, more work is done on the train than in the office.”

‘Foolish’

Saying road, bus and cycle schemes needed improvements as well as rail, Mr Darling added: “The next government and the one after that will be very short of money to spend on the infrastructure that we desperately need.

“To commit ourselves to spending so much on a project that rules out any other major schemes seems foolish. And the costs are not yet nailed down.

“The facts have changed. The case for HS2 was just about stateable in 2010. I don’t believe it is today.”