It emphasises that, after ‘several failed attempts’, Government now believes it has a scheme that is affordable, deliverable and has the support of heritage and environmental groups.

But it urged that present uncertainty around funding be resolved quickly, and described the £1.7Bn scheme as being ‘at the mercy’ of the upcoming Spending Review. This comes after a report by the National Audit Office raised concerns over the cost, timescale and likely benefit of building a road tunnel beneath Stonehenge in May.

“Government plans to open the Stonehenge tunnel by 2026 remain in doubt until a clear decision is made on how to fund the scheme,” said the Public Accounts Committee’s deputy chair Sir Geoffrey Clifton-Brown. “To meet the proposed timetable a funding decision is needed by the end of this year.”

The committee calls on the Department for Transport and Highways England to plan for what alternative arrangements could put in place in the event that the Treasury does not confirm funding this year.

The report also addresses the project’s challenging timetable which includes obtaining planning consents, negotiating with contractors and completing detailed design before construction is scheduled to start in 2021.

In addition, it highlights ambitions to upgrade the entire A303 corridor to dual carriageway and notes that to date just three out of eight projects are committed.

“The Government’s piecemeal approach makes it hard to show the programme is value for money,” said Sir Geoffrey Clifton-Brown. “Unless there is a co-ordinated approach to all eight of the proposed projects there is a risk that traffic jams will be merely shunted along the road.”

Concluding, he said: “It will be extremely challenging to deliver the South West road improvements to cost and time. My committee knows from bitter experience that transport does not have a good record in delivering major projects punctually.”

(Photograph: Highways England)