Pulling the plug on its opposition to the HS2 rail link would be a "monumental betrayal" of the north, Labour was warned today.
Prime Minister David Cameron and his deputy, Nick Clegg, ramped up the pressure on the Opposition to underline its support for the rail link between London and the north after senior party figures appeared to go lukewarm on the plans.
Shadow chancellor Ed Balls insisted today that he still does not believe the case for the £50 billion scheme has yet been made and claimed it would be "completely irresponsible" to sign it off until it had.
" We've always supported the idea of a new north-south rail link, but when I listen to David Cameron and George Osborne giving the impression that, even though the costs are going up billion by billion, and even though the benefits are becoming less clear, they are going to go ahead regardless," he told Radio 5's Victoria Derbyshire.
He added: "W hat I am not going to do is say we support it when the costs are rising, the benefits are unclear and the government are acting like cheerleaders rather than proper stewards of public money."
But Labour was warned it will be letting down the midlands and north as well as businesses and councils by withdrawing support.
Mr Clegg told BBC Radio 2's Jeremy Vine: "I cannot understand why Labour is turning its back on HS2. That is a monumental betrayal of the north by Labour."
A substantial number of Tory MPs are said to be preparing to rebel when the bill continues its passage through the House of Commons while Labour is expected to impose just a one-line whip on the vote.
Mr Cameron, speaking at a press conference in Brussels, said: "I think this is an important national project. I want to see a recovery that is for all, for north and south.
"I don't want to see again a situation where, under Labour, for every 10 jobs created in the south there was only one created in the north.
"This is an important project. It does have all party support. We supported it in opposition when Labour were in government. Labour support it today, as I understand it, now we are in government.
"The Liberal Democrat party support it as well and that is all to the good because these multi-year, multi-parliament infrastructure projects, they can't go ahead without all party support. You won't get the investment, you can't have the consistency.
"So, I believe it does have all party support, I think if Labour are to run away from this they will be letting down the Midlands, they will be letting down the north, they will be kicking sand in the face of council leaders right across the country who want this to go ahead.
"They will be turning their backs on businesses who have been telling us how important it is that infrastructure projects like this go ahead.
"So, if Labour continue to support it, which they should and I believe they will, then of course, it will have all party support and it will proceed.
"I will do everything I can to persuade MPs on all sides of the House that this is important and a good project."
Stop HS2 campaign manager Joe Rukin said: " Ed Balls and his Labour colleagues have kept saying there can be 'no blank cheque for HS2', but a blank cheque is what MPs are due to vote on on Thursday. If they are true to their word they will vote against this white elephant at the earliest possible opportunity and put it out of its misery.
"It seems to us that David Cameron has finally realised what a daft idea HS2 is and is trying to play political games so he can drop HS2 and claim it was all Labour's fault. Instead of engaging in Punch and Judy politics, he should have the courage to admit he was wrong and drop HS2 before more taxpayers' money is wasted on his vanity project."