Keith Parker, an HGV driver from Shropshire, who was following Ian McQueens vehicle northwards on the A7, said he saw the rear of the trailer twitch and then veer of the road into the field.
He told the court a 'black ice' warning was showing in the cab of his vehicle.
When asked why he didn't stop after witnessing the lorry leaving the road, he replied:
"I've never been involved in an accident before"
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