The war of words over the installation of average -speed cameras on the main route to the Highlands has been stepped up amid claims that lorry drivers might renew their threat of driving in a convoy as a "rolling roadblock."

The war of words over the installation of average -speed cameras on the main route to the Highlands has been stepped up amid claims that lorry drivers might renew their threat of driving in a convoy as a "rolling roadblock."

The warning was originally issued last year in a campaign by hauliers and drivers to persuade the Scottish Government to raise the speed limit for heavy lorries from 40mph to 50mph on single carriageways on the A9. They had said they could work with average-speed cameras if the limit was raised.

When ministers agreed to a three year trial with the higher speed limit, lorry drivers called off their action. But there are reports that delays of around 20 minutes in traffic caused by installation of the cameras, have led to drivers considering resurrecting the threat.

The Inverness lorry driver Conor McKenna, who led last year's campaign, said his colleagues were reporting an increase in dangerous manoeuvres because of the delays, with motorists slamming on their brakes when they see the cameras even although they are not yet operating.

He reportedly said: "People don't understand the cameras." And added: "We are looking at a go-slow but I need to speak to more drivers about what is happening."

But Dave Thompson Skye, SNP MSP Lochaber and Badenoch said a convoy protest would be "utterly irresponsible."

He said "The lorry drivers had campaigned for a raising of the speed limit and the government listened. The higher limit will now come into operation in the autumn."