A damning report has accused HS2 rail bosses of hiding information about cost increases and delays.
The parliamentary spending watchdog published its assessment of the high-speed rail project today, accusing the Department for Transport (DFT) and HS2 Ltd of lacking transparency and undermining public confidence.
The public accounts committee said HS2 was "badly off course" and urged the government to regularly update Parliament with "accurate" information.
It said the DFT and HS2 Ltd "were aware of the scale of the issues facing the programme as early as October 2018."
And costs could continue to spiral as lessons from previous transport projects have not been learned, said the MP's report.
Committee chairman Meg Hillier said the cost of community commitments in the first phase of the project had risen from £245m ($296.54m) to £1.2bn.
"There is no excuse for hiding the nature and extent of the problems the project was facing from parliament and the taxpayer."
"The Department and HS2 appear to have been blindsided by contact with reality," she added.
The cross-party committee claim they were mislead by DFT permanent secretary Bernadette Kelly and HS2 Ltd executives Mark Thurston and Michael Bradley.
The report said Kelly "withheld from us that the programme was in significant difficulty" during appearances in 2018 and 2019, "even in response to specific questions."
Hillier, said: “The committee is concerned about how open the department and HS2 Ltd executives have been in their account of this project. It is massively over budget and delayed before work has even begun."
It also said HS2 Ltd's annual report and accounts "similarly failed to give an accurate account of the programme's problems."
The cost of the project set out in the 2015 Budget was just under £56bn, but independent estimates have almost doubled this to £106bn.
Deputy chairman Sir Geoffrey Clifton-Brown said the report was "one of the most critical, in both the transparency of government and the handling of a project, that I have seen in my nine years in total on the committee."
A DFT spokesperson said transport secretary Grant Shapps "has been clear that this project must go forward with a new approach to parliamentary reporting, with clear transparency, strengthened accountability to ministers, and tight control of costs.
"We have comprehensively reset the HS2 programme, introducing a revised budget and funding regime, with significant reforms to ensure the project is delivered in a more disciplined and transparent manner."
The DFT statement added Kelly had acknowledged cost pressures in May 2019 and that discussions between the government and HS2 Ltd "were active and commercially confidential.”