The government has insisted that a review of the cost of a new high-speed railway linking London, Birmingham, Manchester and Leeds is continuing.
The assurances come despite the project reportedly needing an extra £30bn.
HS2 chairman Allan Cook has written to the Department for Transport to warn that the project will exceed the official £56bn budget, the Financial Times reported.
The newspaper cited an internal review for the figure.
“The chairman of HS2 Ltd is conducting detailed work into of the costs and schedule of the project to ensure it delivers benefits to passengers, the economy and represents value for money for the taxpayer,” the Department for Transport said in a statement.
“This work is ongoing. We expect Allan Cook to provide his final assessment in due course.”
An HS2 Ltd spokesperson said: “We don’t comment on leaks or speculation. We have previously noted that our chair, as you would expect, continues to scrutinise the programme, and regularly reports back to the Department.
“We are determined to deliver a railway that rebalances the economy, creates jobs, boosts economic growth and is value for money for taxpayers.”