A Government heavyweight has rubbished claims average speed cameras will save lives on the A9.
UK Cabinet minister Danny Alexander has waded into the debate and called for an urgent rethink.
Describing the plans as “knee-jerk decision”, the Chief Secretary to the Treasury demanded evidence that the £2.5 million scheme would prevent accidents.
In a letter to Scottish transport secretary Keith Brown, Mr Alexander also claimed that a £1.1 billion cash pot was available to bring forward dualling plans, which are currently timetabled to finish in 2025.
Cameras which measure speeds over set distances are due to be installed on a 136-mile section between Dunblane and Inverness by next summer in an attempt to cut the casualty toll on the road.
Mr Alexander, who is MP for Inverness, Nairn, Badenoch and Strathspey, said he was “surprised” when the proposals were announced last month.
Although he agreed that speed was a “significant” factor in making the A9 Scotland’s deadliest road, he revealed he would only support the targeted use of speed cameras at accident hotspots, rather than along its entire length.
While Mr Alexander’s response has won the support of protesters campaigning against the average speed cameras, he has come under fire from Mr Brown.
A spokesman for the transport secretary hit back, saying: “This is the height of hypocrisy from Danny Alexander, given the Liberal Democrats’ utter failure to commit to dualling the A9 during the years they were in office in Holyrood.
“People know that Mr Alexander’s first loyalty is to the Treasury, not to the Highlands and its transport needs, something underlined by his failure to fight properly to protect key flights to the region.”
The Scottish Government also denied his claims that money from an infrastructure fund was available for dualling works.
They said the £1.1 billion “merely reversed some of the cuts imposed by the UK Government”.