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.
It comes after Ed Balls said the £50 billion 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.
The peer 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."
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 cannot say that your principles 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."