A £50bn rail scheme that could cut journey times between London and Glasgow risks being poor value for taxpayers' money, MPs have warned.
Members of the Commons Public Accounts Committee also warned the cost of the High Speed 2 project could spiral.
And they criticised ministers for the continued failure to produce a report on whether or not the line should extend into Scotland.
Their report calls for a UK-wide rail plan, to guide major infrastructure projects for decades.
The PAC warns: "We are sceptical about whether the Department for Transport (DfT) can deliver value for money for the taxpayer on HS2."
Members are not clear the scheme is "part of a clear strategic approach to investment in the rail network".
Evidence that decisions were being made without such a plan could be seen in the fact that "the department has still to publish proposals for how Scotland will benefit from HS2, including whether the route will be extended into Scotland," they suggested.
A Department for Transport spokesman said: "HS2 will have a transformational effect, rebalancing the economy and helping secure the UK's future prosperity, providing high value for money to the taxpayer.
"With Sir David Higgins as chairman of HS2 Ltd, we are fully focused on keeping costs down and are determined that this vital part of the Government's long-term economic plan will be built on time and within budget.
"As the project moves forward towards construction we will continue to address the issues raised by the committee, and in particular value for money."
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