Treasury Secretary Danny Alexander has rounded on critics of HS2 by saying the £50 billion high-speed rail project is essential for Britain.
But he also appeared to indicate there was a possibility there might not be enough time to get the HS2 Hybrid Bill through Parliament before the 2015 General Election.
In the last few days, Labour has appeared to be cooling towards the scheme, with shadow chancellor Ed Balls questioning whether it might be better for the money to be spent on other schemes.
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He told his party's annual conference he would not "write a blank cheque" for the scheme, which has a first phase with a high-speed line passing through Tory heartlands from London to Birmingham.
Speaking at an Institution of Civil Engineers transport conference in London Mr Alexander said HS2 and the coalition Government's other transport projects were "absolutely essential to the long-term future of our economy".
In a dig at those going lukewarm on the scheme, he added: "It would be absolute folly to neglect these long-term benefits for short-term political reasons."
He said HS2, which has a current budget of £42.6 billion with a further £7 billion earmarked for the trains, could be delivered on time and possibly below budget.
Mr Alexander said it was right that such projects should be kept under close scrutiny, adding that there was "enormous project management expertise in this country".
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In a question-and-answer session, Mr Alexander was asked about the speed of the HS2 Hybrid Bill which will go through Parliament following a Paving Bill.
He said the Government would make sure the Hybrid Bill was delivered "as quickly as possible".
Mr Alexander went on: "Our intention is to get the Hybrid Bill well on its way during this Parliament. We would certainly like to get it as far as possible during this Parliament."
One questioner, interpreting these remarks as an admission that the legislation might not be completed before the May 2015 General Election, asked what was likely to happen to the Bill if there was a change of government.
In reply, Mr Alexander appeared to backtrack on his earlier remarks by saying: "It is our intention to get it (the Bill) through this Parliament."
Later at the conference, HS2 Ltd chief executive Alison Munro said she envisaged the scheme being on time and within budget.
She went on: "We have never asked for a blank cheque, neither do we want or need one.
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"We fully understand the need to keep costs around the project under control. We look forward to bringing HS2 home, on time and within budget."