Former transport secretary Lord Adonis warned Labour not to ditch its principles for short-term political gain amid speculation it will drop its support for HS2.
The Labour peer, who mastermind the high-speed north south rail link, told the party it could not “preach long-termism” and then fail to practice it.
The prospective high-speed rail link will cut through large sections of South Northamptonshire.
His remarks come after Ed Balls suggested the £50 billion earmarked for HS2 could be spent on housing and other transport projects and warned he would not “write a blank cheque” for the scheme, fuelling speculation that Labour is poised to pull its backing.
At a Progress fringe event in Brighton on Tuesday morning, Lord Adonis said: “I’m very mindful of HS2 and where we are on this too.
“We cannot as a party preach long-termism and not practice it ourselves. We have got to be very clear about that.”
He added: “We are the party that started HS2. I published the plan three and a half years ago. We set the whole thing out, we set out the rationale, including capacity.
“We went through the whole thing. We did a major job of work.”
He added: “You have got to in politics, you cannot say that your principles and all that apply to other people but they don’t apply to you when short term political advantage might rear its head. We have got to stick with this. It’s very important.”
Mr Balls appeared distinctly lukewarm about the project yesterday calling for an injection of “hard thinking” on the plans and highlighting the spiralling costs.
Pressed after the Progress event about the changing tone coming from the shadow chancellor, the peer said: “The Government does need to demonstrate real cost control, instead of which the last thing they did was to increase the budget by £10 billion.
“I have always been clear there has got to be proper cost control and proper value for money.”
Shadow transport secretary Maria Eagle said Labour “support” HS2 but called on David Cameron to “get it back on track”.