Could London have a new underground line by 2030? And does it need it?
Plans for a diagonal route from the north east to the south west went on show today, with the catchy title of Crossrail 2.
Our Political Correspondent Simon Harris has more.
Transport for London has backed the plan to build a second Crossrail link across London. The organisation says a new link is needed because of population growth and the extra passengers using Euston after the High Speed Two rail link is finished to Euston.
But TfL's Managing Director for Planning, Michele Dix, says construction on Crossrail 2 will only start after the first Crossrail link is finished in 2018.
Val Shawcross, the London Assembly Labour Transport spokesperson, responded to the proposal to build a new North-South Crossrail link: