The National Audit Office (NAO) has launched an investigation into overspending and delays to Crossrail.
The NAO will examine the causes of the cost hikes and delays that saw the opening date slip by at least nine months from this December to autumn next year.
In a statement, the NAO said: “Our investigation will examine the causes of the cost increases and schedule delays, the terms of the additional funding, and the governance and oversight of the programme.
“We will also examine the steps being taken by Crossrail Ltd, TfL, and the [Department for Transport] to minimise the impact of the cost increases and delays.”
Crossrail has suffered a number of cost and schedule setbacks in recent months.
In July, the government announced that the overall funding for the project had increased by £590m to £15.4bn, with the additional cash needed to complete remaining work on its central section.
The nine-month delay to Crossrail’s opening was confirmed at the end of August, which CN revealed was driven by delays to the fit-out of its new central stations and tunnels.
And in October, Crossrail was given an extra £350m loan by the government to support construction and testing work.
Earlier this month Crossrail appointed Mark Wild as its new chief executive, replacing Simon Wright at the helm of the project.
Crossrail said Mr Wild had been brought in to lead the project through its final phases, which include trial running, trial operations and the opening of the central section.
Mr Wild, who has served as London Underground MD since June 2016, will return to his role at the transport body once the Elizabeth line has opened.
The appointment was followed by the news that delays to Crossrail were set to cost TfL £210m.
The client will miss out on around £20m during the current financial year to April, with a further £180m-£190m in the following 12 months.
TfL and the Department for Transport have commissioned independent reviews into Crossrail’s governance and financing, which are being carried out by KPMG.
A spokesperson for Transport for London said: “We will fully assist the National Audit Office with its investigation into the Crossrail project, which is jointly sponsored by TfL and the Department for Transport.”
A DfT spokesperson said: ”Crossrail, a wholly-owned subsidiary of Transport for London, is a world-class project that will transform journeys across the South East and add £42 billion to the UK economy.
“We welcome the NAO investigation and stand ready to assist.”
Crossrail has been contacted for comment.