David Cameron held out an olive branch to Labour over the troubled high speed rail line as he pledged to ensure the cost of the network was cut.
Speaking at the annual conference of the CBI in London, the Prime Minister said it was vital the UK built a new railway to the North.
Trains are currently due to run between London, Birmingham, Manchester and Leeds, while the Government launched a review last week to consider whether the high speed line should be extended into Scotland, including whether trains should stop at Newcastle.
Under the current plans, the network and the new trains required have a total estimated cost of £34bn, plus an extra £16bn in contingency funding which ministers say is unlikely to be spent.
The proposals were drawn up by the last Labour government and all parties agree they can only go ahead with cross party support because the scheme will take so long to build.
But Labour Shadow Chancellor Ed Balls is reviewing its support for the project because it is concerned about the rising cost.
Speaking to the CBI, Mr Cameron accused Labour of “betraying” the North and Midlands - but he also revealed that HS2’s new chairman, Sir David Higgins, would look at ways of reducing the cost.
He said: “Those who want to delay or obstruct HS2 show a lack of vision. They are playing politics with Britain’s prosperity. They are betraying everyone north of Watford. And they want to condemn Britain to the slow lane.”
The Prime Minister suggested that Sir David, who was chief executive of the body responsible for organising the 2012 Olympics, would get HS2 built “on time and on budget”.
Mr Cameron added: “He has agreed that the first vital step will be to bring his penetrating eye and expertise to a specific task. To report on the costs. And to maximise the benefits for all parts of the country as quickly as possible.
“He has already said the line could come in ‘substantially’ under the current budget. And he has also made it clear he needs cross-party support to do it.”
Mr Balls, speaking at the same event, insisted he was right to question the cost.
“The Labour Party cannot – and will not - give the government a blank cheque. That is what you would expect from any credible official opposition seeing a Government desperately mismanaging a project. And that is what is happening here with the costs having shot up to £50bn.”