It said the revised schedule and budget agreed for Crossrail in April 2019 was unachievable because the programme was further from being complete than Crossrail Ltd and its other sponsors understood.
Although cost increases and schedule delays are in line with Crossrail Ltd’s 2020 estimates, they exceed the available budget and there are still significant issues that could arise as the railway is brought into service, the NAO said.
The joint sponsors for Crossrail are the Department for Transport and Transport for London (TfL), while Crossrail Ltd, a subsidiary of TfL, is responsible for delivering the programme.
When the NAO last reported in May 2019, the funding package for Crossrail stood at £17.6bn, the forecast cost was £17bn, and the central section of the Elizabeth line was due to open by March 2021 at the latest.
But since then, milestones have been repeatedly missed in 2019 and into 2020 due to Crossrail Ltd continually uncovering problems or...