The most significant line in Ed Balls's speech to the Labour conference was on HS2. Having previously warned that there would be no "blank cheque" from his party for the new high-speed line, he went further today, questioning whether it was "the best way to spend £50bn for the future of our country".
Under this government the High Speed 2 project has been totally mismanaged and the costs have shot up to £50bn. David Cameron and George Osborne have made 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 project.
Because the question is – not just whether a new high-speed line is a good idea or a bad idea, but whether it is the best way to spend £50bn for the future of our country. In tough times it's even more important that all our policies and commitments are properly costed and funded.
The signal from Balls that Labour is actively considering withdrawing support from the project raises the possibility of a major party split over the issue. Andrew Adonis, the former transport secretary and the architect of HS2, recently argued  in the New Statesman that it would be an "act of national self-mutilation" to cancel the programme. As the party's shadow infrastructure minister and the head of the party's growth review, he remains a significant figure and would likely have to resign his post if Labour came out against the project.
In his piece, Adonis warned that the urgent need to increase rail capacity (the West Coast Main Line will be full by 2024) meant there was "no free lunch - or pot of gold which can be diverted to other projects in anything but the very short-term, with more costly consequences thereafter". But many in Labour would like to transfer funds from HS2 to a mass housebuilding programme. It would allow the party to differentiate itself from the Tories while remaining within George Osborne's fiscal envelope. Today, Balls made it clear that he is sympathetic to their demands.