Labour has delivered another blow to the future of the HS2 line by saying it would re-examine the project if the party is voted back into power.

At the Labour party’s annual conference, shadow chancellor Ed Balls said the government had ‘mismanaged’ the project and had allowed costs to spiral.

He also raised questions about the future of HS2 during his main speech to delegates on Monday.

“Under this government, the HS2 project has been totally mismanaged and the costs have shot up to £50billion,” he said.

“David Cameron and George Osborne have made it clear they will go full steam ahead with this project, no matter how much the costs spiral up and up.

“They seem willing to put their own pride and vanity above best value for money for the taxpayer.

“Labour will not take this irresponsible approach. So let me be clear. In tough times, when there is less money around and a big deficit to get down, there will be no blank cheque from me as a Labour chancellor for this project, or for any other project.”

This follows a series of setbacks for the project during the past month, with criticism from the Institute of Directors and other Labour politicians, and an estimate from the Institute of Economic Affairs that the scheme could end up costing at least £80bn.

Mr Balls’ comments have been welcomed by campaigners.

Stop HS2 member Joe Rukin said: “We are ecstatic that the shadow chancellor is looking seriously at the cost of HS2 and whether the project is worth it, as opposed to the coalition, who seem to be saying that no matter what the cost, we can’t afford not to build it.

“As the costs of HS2 have gone up, and will continue to go up, Ed Balls is dead right to question whether HS2 is worth it.”

Councillor Ray Puddifoot, leader of Hillingdon Council, added: “The Labour party can’t bleat on about benefits and countenance this sort of project. They are gearing up to drop it altogether in my view. Sooner or later, people will realise what the alternatives are. The money should be spent on current infrastructure.”

Lottie Jones of Ruislip Against HS2 was encouraged by Mr Balls’ declarations.

“It is a relief to hear other politicians speak about it in negative terms.

“We are getting closer to an election, and they are starting to realise that they need to win votes. It will be a political hot potato.

“I think [Ed Balls] was kite-flying and gauging the reaction, and although he didn’t say outright that Labour would scrap it, that was the implication.

“It is very much in people’s consciousness nationally now, and it has been a great summer for everyone who is against HS2.

“Ed Balls has fired the first shot, but who will have the guts to shoot this white elephant?”