Cost of upgrading six miles of A9 near Inverness rises to £308m

Two sections of single carriageway totalling 11 miles (18km) of road have been upgraded over the past decade under the £3bn dualling project.

But 77 miles (124km) of the route has still to be dualled.

When completed, the new Tomatin to Moy section would provide about 20 miles (33km) of continuous dual carriageway between Inverness and Slochd.

The project has been hit by delays, including earlier this month when it was revealed the section was expected to be operational in 2028 and not late 2027 as hoped.

Last year, the construction contract was re-tendered after only one company bid for the work.

In July, the Scottish government agency awarded the contract worth almost £185m to Balfour Beatty Civil Engineering Ltd.

The new report said inflation and costs around a change in contract procurement had led to the increased estimated total cost of £308m.

Mr Ewing said the Scottish government “needed to be candid” with the public on costs.

He told BBC Scotland News: “A full explanation is needed to say why the whole costs were not mentioned in the recent press release.

“The total cost will, I expect, include all preparatory work in route selection, and design, obtaining the necessary legal orders.”

Mr Ewing added: “But until such time as the total business case figures are broken down into components and made public, we remain in the dark.”