Rather than risking the blame for killing the project, Labour has decided to take the credit for saving it by forcing the government to reduce costs.
The shadow chancellor never said that there would be no recovery, only that it would be painfully slow. And he was right.
While restricting current spending, the party should promise to invest the proceeds of growth into future-facing areas like skills, childcare and infrastructure.
The shadow chancellor writes to Osborne as Treasury select committee chair Andrew Tyrie says that OBR auditing could "enhance the quality of public debate".
The architect of High Speed 2 and the head of Labour's growth review says that Ed Balls's threat to withdraw support for the project has "raised the bar".
Andrew Adonis, the head of Labour's growth review and the architect of the project, has warned that cancelling the programme would be an "act of national self-mutilation".
Osborne's instinct will be to use the extra revenue for faster deficit reduction or tax cuts. But Labour can argue for an alternative centred around investment.
Osborne is determined to claim that there is a "black hole" in Labour's spending plans, whatever the Office for Budget Responsibility may say.
Asked to choose between a third runway at Heathrow and High Speed 2, Balls replies: "third runway". Miliband would say the reverse.
The opposition should worry less about the growth rate and more about developing its own story about the economy.