Transport secretary, Chris Grayling, has revealed that the cost of the Crossrail project has risen yet again. In a written ministerial statement, Grayling said that work on track and stations on the overground section to the west of London, being carried out by Network Rail, has run a further £210m over budget since costs were updated in 2018, bringing the total cost of the project to date to more than £17.8bn.

Grayling said the cost would be met from Network Rail’s own budgets but given the fact that it is a state-owned body, the additional cash is effectively taxpayers’ money. “The coming months will be critical for the project as Crossrail Ltd work to complete the installation and integration of the tunnel, stations and signalling systems, and Network Rail continue their works on surface sections of the route,” said Grayling.

“It remains a hugely complex project and uncertainty and risk remains across the programme, with significant testing and integration work remaining, he said.

Network Rail has a relatively small portion of Crossrail work and the news of these confirmed cost overruns – now more than 20% over its own allotted £2.3bn budget for Crossrail – will further fuel fears amongst MPs that the delayed project could end up costing significantly more yet. Network Rail blamed the additional time taken to deliver the project for the additional costs.

Back in May, the National Audit Office (NAO) said there had been “clear damage” to public value because of changes to design, delivery schedules on Crossrail and an “unrealistic” commitment to delivering the new service by December 2018.

NAO boss Amyas Morse said: “Throughout delivery Crossrail clung to the unrealistic view that it could complete the programme to the original timetable, which has had damaging consequences. There have been a number of choices made in the course of this project that have clearly damaged public value.”

Crossrail bosses have highlighted what they call a “six-month delivery window” for completion of the project, saying “many risks and uncertainties remain.” The earliest date for completion is October 2020 and the latest March 2021.