MPs say plans to build a road tunnel near Stonehenge are at risk, unless money for the project can be secured.
They've issued the warning as part of a report from The House of Commons' Public Accounts Committee.
Public private finance was due to fund the scheme, but the government cancelled all future deals using that model last year.
The tunnel is a key part of plans to dual the A303 and there's been warnings without it then the benefits of other aspects may be less financially viable.
A report concludes: "If uncertainty about funding is not resolved before 2020, the timetable and viability of Stonehenge tunnel project will be put at risk.
"The Stonehenge tunnel project was to be financed under the PF2 private finance initiative but in October 2018, the Chancellor cancelled future private finance deals, including for this project.
"The Department says that it and HM Treasury remain committed to the project and the Treasury has released funding of £21.5 million during 2019-20 to allow the project to keep going.
"However, the Department does not expect to fund the project from its £25.3 billion draft funding envelope for the second Road Investment Strategy (2020 to 2025). It intends to make a case to HM Treasury for additional funding for the project as part of the next Spending Review, the timing of which is still uncertain.
"The Department says that only having a one-year settlement would raise questions about whether the scheme could continue to the same timeframe.
"Highways England says that it must have funding certainty by the end of the year if it is to begin the commercial process to find a construction contractor in the first quarter of next year and keep to its 2026 target opening date.
"It says that without funding clarity, potential suppliers will not be willing to incur the high bidding costs involved.
"The Department's view is that “if we want this scheme to continue, and to continue in a sensible and efficient way to the current project timeframe, we cannot wait another year, or however long it takes to carry out a spending review."
The report recommends: "The Department and Highways England must plan for what alternative funding arrangements or delivery plans it could put in place, in the event that HM Treasury does not confirm longer term funding by the end of the year."
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