Warnings that Crossrail would be delayed were deleted by Transport for London (TfL) in notes prepared for mayor Sadiq Khan, the project’s former chairman said.
Sir Terry Morgan claimed information that there would be insufficient time to complete testing on the new east-west railway line was removed from documents being sent to Mr Khan.
He told the London Assembly Transport Committee that the weekly briefings were “cleared” by TfL before reaching the mayor.
Following the hearing, a TfL spokeswoman said the briefings being sent to Mr Khan were TfL reports providing a “snapshot of the status of the project”.
Sir Terry also revealed that TfL had told him “what to say” at a TfL board meeting on July 25.
He offered to supply Assembly members with a copy of the document, which he said “took out any reference to not being able to deliver the programme in 2018”.
This is “completely untrue”, according to TfL.
The transport body insisted that prior to the July 25 meeting Sir Terry “went through what he intended to say and subsequently asked if someone would write this up as an aide-memoire for him to use”.
Sir Terry’s comments come amid controversy over whether Mr Khan knew Crossrail would fail to open as planned in December 2018.
Sir Terry said Crossrail Ltd had a board meeting with TfL officials on July 19 last year in which it was concluded that “delivery in 2018 was not feasible”.
This information was shared with the mayor on July 26 and was “a very clear indication” of the delay, he told the committee.
Mr Khan has previously insisted he only found out about the delay on August 29, two days before Londoners were informed.
Mark Wild, who became Crossrail Ltd chief executive in November, told the committee that “none of the stations could have been ready for December”.
He added: “There is still thousands of hours of construction work to do in the tunnels.”
No rescheduled date has been set for when services will begin.
Once fully opened, Crossrail will be known as the Elizabeth line and will run from Reading and Heathrow in the west to Shenfield and Abbey Wood in the east, via 13 miles of new tunnels in central London.
The budget was set at £15.9 billion in 2007, but this was cut to £14.8 billion in 2010.
It was confirmed in December that the project had been given a £1.4 billion bailout due to the delay.
Crossrail’s cost is being met by the Government, the Greater London Authority and London businesses.