A leaked government report argues HS2 should be built despite it costing tens of billions of pounds more than first predicted and providing less benefits.
The government should stump up £88bn for the full high-speed rail project to connect London, Birmingham, Leeds and Manchester, the document seen by The Times suggests.
Author of the report Douglas Oakervee, former HS2 chairman, recommends spending £32bn more than the government budgeted for the project back in 2015.
The ballooning costs render the high-speed network less of a benefit to taxpayers - the public returns on investment falling from £2.30 for every £1 spent in 2017 to between £1.30 and £1.50 for every £1 spent this year.
Mr Oakervee also pointed out that the procurement strategy for the first phase of HS2 had been a failure and prices had been inflated.
Despite these issues, the former president of the Institution of Civil Engineers argued the project is still essential to ease the burden on other lines.
Without HS2, huge ticket price rises would be needed to discourage too much travel at peak times.
The leaked report will put pressure on Prime Minister Boris Johnson to decide whether to press ahead with the project, rather than continuing to delay the decision until after the General Election on December 12.
Many leading Conservatives have criticised the report for suggesting what would be the biggest infrastructure project in Europe goes ahead.
Amongst the critics is Labour peer Lord Berkeley, former deputy chairman of the review panel, who is preparing a dissenting report to be shown to the Prime Minister.
