The London Assembly says that the role of reviewers needs to be “clearly and fully built into the governance structure” and that their influence could help to “provide assurance of deliverability and protect the public purse”.

The Assembly also calls for greater “transparency and openness” on both Crossrail and future projects, balancing optimism to keep staff motivated with a “reliable communication of risk, productivity and project performance”. Decision making should also occur in formal meetings open to the public, it says.

Other recommendations following the delay with completing Crossrail include keeping designs simple and incorporating standard rather than bespoke features to reduce risks to budget and timelines.

It adds that sponsors on future schemes should ensure governance systems are fit for purpose throughout a project and be reviewed periodically, especially when there is a clear shift from one stage of a project to another, such as from construction to fit out to operation.

Skills needed throughout the lifetime of a project should also be reviewed, it says, to ensure the right technical capability is present at each stage.

The Assembly also calls for the Mayor to strengthen control over Transport for London and recommends that the Commissioner Mike Brown “reflects on whether he is fit to fulfill his role” at TfL.

This latest review of Crossrail comes after the central section’s opening slipped from December 2018 to a date that has yet to be confirmed. The review claims that significant concerns raised by an independent reviewer as early as January 2018 were largely ignored and that the desire to achieve the completion date “overpowered any professional and critical assessment of risk”.

London Assembly transport committee chair Caroline Pidgeon said: “It is a complete tragedy that one of the most highly anticipated engineering projects the world has ever seen has found itself in a mess of overspending, mismanagement and an embarrassingly long delay.

“The inability of senior figures in the project to push past their obsession with a December 2018 launch date is one of the main reasons why their dream did not become a reality.

“Crossrail will provide immeasurable benefits to London once launched, but vital lessons must be learned by the Mayor, TfL and Crossrail so we all can bring this sorry chapter of the project’s journey to a close.”

In a statement, a spokesman for Crossrail said: “A new leadership team and enhanced governance structure has been put in place to strengthen the Crossrail programme. We take the views of the Assembly Transport Committee seriously and will be reviewing the recommendations that are applicable to Crossrail Ltd carefully.”

Transport for London said: “It is clear that the responsibility for the delay to the Crossrail project lies with the former management of Crossrail Ltd. Everyone involved is fully focussed on completing the project and opening the Elizabeth line to passengers as soon as possible.”