The way Crossrail was managed added an extra £2.5 billion to the cost of the project, a new report has revealed.

Crossrail – also known as the Elizabeth Line extension – is set to run from Reading and Heathrow into central London and then through to Shenfield and Abbey Wood in the east.

The project is jointly funded by TfL and the Department for Transport with the implementation managed by Crossrail Ltd.

The line was supposed to have opened in December 2018 but in August the same year it was announced it would not be opening until autumn 2019.

Earlier this year Crossrail Ltd admitted it could not commit to an opening date.

Now a new report by the National Audit Office (NAO), released today, said the extra costs incurred were caused because the team managing the project had a “fixation” with opening the line in December 2018, which then impacted on its decisions regarding the project.

The total cost of the project has now reached £17.6 billion, with additional costs caused by changes to contractor’s delivery schedules and designs, according to the NAO.

Caroline Pidgeon, the chairman of the London Assembly transport committee, said: “Going forward Crossrail, TfL and the Mayor must be realistic, pragmatic and honest with themselves and Londoners about any issues that occur and deal with them accordingly.

“They should not be afraid to face the music if a big stumbling block threatens the timing of delivery.

“Crossrail is a huge and complex project and it is understandable that not everything will go to plan.

“However, we must leave behind the days of chasing an opening date and focus on the successful delivery of a new line for Londoners.”

The cost of some Crossrail stations was also six times higher than expected the report said.

The cost of Whitechapel, for example, rose from £110 million to £659 million, a 499 per cent increase, making it the most expensive station on the line.

The NAO also said there was “no going back” as £16 billion had already been spent and also said it was not possible to assess Crossrail’s value for money to the taxpayer until it opened.

The chief executive of London Chamber of Commerce and Industry, David Frost, said the report showed how Crossrail was always going to be a “complex” and “challenging” project and “highlights past management failings”.