Crossrail's budget overshoot could surpass £1bn as the flagship project works towards a new 2019 deadline.
Last week it was confirmed that the £15.4bn Elizabeth Line, which stretches from Reading and Heathrow in the west to Shenfield and Abbey Wood in the east, has been delayed by almost a year over safety issues and will now not open through central London until next Autumn.
In light of the new deadline, one industry source told City A.M. that the budget overshoot could "well exceed £1bn by another billion".
They said the delays had their roots in the concept of Crossrail changing from an extension to the Underground "to a fast East-West urban rail link", and that those complexities were compounded by frequent changes in management.
A spokesperson for TfL said: "Crossrail Limited have just informed TfL and Department for Transport (DfT) about the delay. Crossrail Limited are working to establish any additional impact on funding from the revised schedule."
The Elizabeth Line’s was originally forecast to cost £14.8bn. In July the transport minister Jo Johnson confirmed the overrun had swelled by £590m owing to "cost pressures".
City A.M. understands that Crossrail made the decision to hold off the project on Wednesday last week and only told TfL and the DfT, which are joint sponsors of the project, the following day.
The delay to the Elizabeth Line will be a severe blow to TfL, which was banking on the line to boost its revenues.
Earlier in the year the former deputy mayor for transport, Val Shawcross, warned that delays to the project were the "biggest revenue risk to TfL", which is already facing a £1bn operational deficit and declining passenger numbers.
A TfL spokesperson added: "We are assessing the revenue implications. Details of how we will manage the change will be announced as part of our annual business planning process at the end of 2018."