Former Crossrail chairman Sir Terry Morgan has confirmed he will publicly give his account of events before delays to the rail project were announced.
Sir Terry claimed that mayor of London Sadiq Khan knew a December opening would not be possible months before it was announced.
At a London Assembly transport committee hearing last month, Mr Khan accused the former chairman of having said a “number of things which are simply untrue” and of “misremembering” events.
Afterwards, committee chairwoman Caroline Pidgeon said: ”It is very frustrating that despite a long meeting, with summonsed documents, the mayor and the TfL commissioner speaking at length, we’re still far from understanding who knew what and when.
“Someone between these two parties [Mr Khan and Sir Terry] is not giving a full account and we will stop at nothing to get to the bottom of this.”
Sir Terry will face questions at the same venue.
Tony Meggs, the former head of the Infrastructure and Projects Authority and incoming Crossrail chairman, will also face questions from the Assembly on Wednesday alongside chief executive Mark Wild.
Mr Khan accused Crossrail of a governance failing over the manner in which delays were revealed.
Among the issues causing delays to the project are integrating trains onto lines which use three different signalling systems.
The previous hearing also heard that TfL will attempt to use simpler systems with Crossrail 2 as a result.
There is currently no date set for Crossrail’s opening, after a further delay was announced last month.