Transport for London (TfL) boss Mike Brown ordered references to the difficulties Crossrail was experiencing with dynamic testing to be removed from email updates sent to Sadiq Khan, it was revealed today.

At a grilling by the London Assembly's transport committee, Howard Smith, operations director for TfL Rail and the Elizabeth Line, admitted he felt Crossrail ought to brief the London mayor that there was insufficient time to carry out dynamic testing.

The London Assembly has been able to get hold of key emails exchanged between senior members of TfL and Crossrail as part of its investigation into the railway's delay, which was revealed last summer.

The £17.6bn Elizabeth Line was originally scheduled to open last December but has been delayed indefinitely due to time and cost pressures.

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Tom Copley, a Labour Assembly member of the committee, read out one particular email dated 19 June, in which he said Smith appeared to be "quite adamant that this needed to be included".

"I'm wondering why you think it was taken out, as it transpired, by Mike Brown?"

Smith said a paragraph that referred to the time constraints around signalling testing should be included in an update to the mayor.

The email read: "Removing the statement re insufficient testing time is wrong. If it's Andy or Steph who've done so I think you need to explain that we (one) see it is a critical issue that we need to note. I'd remind them that we have been taken to task (on stage two) for not highlighting risks. If it's Mike I don't think it changes my view but he is the boss."

The Crossrail crisis reached a height in September when the London Assembly accused Khan of misleading the public about what he knew and when about the delay. The mayor has maintained that he was only informed of the delay to Crossrail two days before it was publicly announced on 31 August last year.

Copley then asked if there was a general culture at Crossrail and TfL of people lower down the chain of command not wanting to send information further up out of fear of the reaction.

"I think more widely, probably yes," Smith replied.

"When we go back over Crossrail history we will find occasions of that happening. But do I think that email itself is direct suppression of something vitally important? No."

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A TfL spokesperson said: "TfL produced regular reports for the mayor, drafted with input from Crossrail Limited and London Underground’s Elizabeth Line team.

"There were rare occasions when it was felt that information should not be included as a simple line in a weekly report but needed detailed explanation at regular face-to-face meetings, including details of the planned remedial action to be taken.”