Alastair Darling, the former Labour chancellor, has launched a vicious attack on the HS2 high-speed rail project, dismissing its economic benefits as "highly contentious".
Darling, also a former transport secretary, said HS2 "ran the risk of substantially draining the railways of money over the next 30 years".
Warning that political visions "can easily become nightmare", the former chancellor added that it seemed "foolish" to commit to a project that ruled out any other major schemes.
His comments in the Times come on top of previous concerns he has expressed as recently as last month, when he warned there was an "awful lot wrong" with the £50bn project.
The former Chancellor's stronger intervention comes weeks after former business secretary Lord Mandelson dismissed HS2 as an "expensive mistake" and "damaging to the northern regions".
Despite the current estimated £50bn cost, a series of reports have suggested the cost could be far higher. An Institute for Economic Affairs (IEA) report earlier this week estimated the eventual cost at £80 billion and the Treasury is said to be working on a figure of £73 billion.
Darling wrote: "It is time to revisit the case for HS2. 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."
"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."
Questioning the cost of HS2, Darling asked: "If you gave England's four biggest cities £10 billion each for economic development could they spend it on HS2?"
Saying road, bus and cycle schemes needed improvements as well as rail, 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."