The NAO is set to begin an investigation into the cause of the £16bn scheme’s delay early next year

The National Audit Office has confirmed it will be launching a probe into Crossrail’s delay.

In a notice published on its website, the public sector watchdog formally announced that it would launch its investigation into the £16bn rail project early next year.

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, Transport for London, and the department [for transport] to minimise the impact of the cost increases and delays.”

The probe was mooted in a letter London mayor Sadiq Khan sent to the NAO flagging concerns about how Crossrail is being run.

The letter, seen by Building yesterday, said Khan has instructed TfL to provide any support to the NAO’s review, which at that stage was unconfirmed, that the watchdog would find helpful.

Khan wrote: “I know that the remit of the National Audit Office does not extend to the Greater London Authority or TfL, but clearly, I have a strong interest in learning those lessons both as a joint sponsor of the Crossrail project and as the Mayor of London in the context of the significant pipeline of infrastructure investment that is needed to support our city’s growth.”

In the same letter Khan suggested Crossrail executives had either misled him or failed to anticipate delays and further cost overruns.

Khan said he believed a £300m sum handed over to Crossrail in July would ensure the Elizabeth line was opened in December 2018 as planned  following repeated assurances from senior Crossrail figures but that “we [DfT and Khan] now know that the scale of the issues faced was in fact much greater”.

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