Sadiq Khan faces fresh scrutiny over Crossrail delay after July dossier emerges

London mayor Sadiq Khan is facing fresh questions over what he knew about the delay to Crossrail following the emergence of a dossier from July that indicated the £15.4bn project would not open on time.

Khan has repeatedly said that he was only informed of the delay two days before it was made public on 31 August, but the London Assembly has argued that Khan must have known about the delay during a series of meetings in July.

The assembly's transport committee accused Khan of misleading the public over what he knew about the delay, saying in a letter to the mayor that accounts of the delay had been "partial and contradictory".

The Sunday Times first reported the existence of the dossier, which emerged in July and indicated that the Elizabeth Line, which will stretch from Heathrow in the west to Abbey Wood in the east, was unlikely to open in December, as planned.

In a recent letter to the National Audit Office, which is investigating the delay, the mayor said he still had "serious concerns" about the "transparency and effectiveness of Crossrail's governance" following the fallout from the delay.

"From July, there are now three TfL and two DfT non-executive directors on the Crossrail Ltd board," he wrote. "However, since then – and with the latest revelations about the project's cost and schedule – I continue to have significant concerns over transparency on the project and the effectiveness of Crossrail's governance, strategic risk management, commercial arrangements and assurance regime."

A spokesperson for Khan said: "Crossrail revised their schedule at the end of August and this was the first point at which the mayor was advised of an opening date for the central section.

"It is not true to say that Crossrail told the mayor in July that they had taken the decision to rule out a December opening date.

"Briefings given to the mayor during July included potential implications of Crossrail's cost and scheduling pressures not being resolved – contingency planning you would expect with any project of this size and importance."

The cost of the Crossrail delay to TfL's already hard-hit finances have become clear. The London Assembly's budget committee was told earlier this month that TfL would lose £200m because the railway will not open on time.