This law should be changed because it is very out of date. It was introduced when braking systems on lorries were incapable of coping with braking at speed. Modern lorries are now fitted with disc brakes & abs systems. Lorries should be allowed to keep up with the flow of traffic instead of restricting it. To many accidents have been caused by impatient car drivers taking risks to overtake a slow moving lorry.
Abolish the 40mph speed restriction on single carriageway A roads for Large/heavy goods vehicles.