Petition Road tax for all agricultural vehicles

Agricultural vehicles use public highways but do not pay road tax and do not pay full duty on fuel. How is this fair when every other business in the UK has to? When the original decision not to tax agricultural vehicles was made only a small amount of equipment used the roads but now farmers use them regularly and not solely for agricultural purposes. Tractors can now pull as much as many lorries and are used for hauling all manner of equipment without the inconvenience of expensive commercial tax. Quad bikes are used on the roads though not taxed or MOTd like private bikes.
Private road users have to pay tax according to the environmental impact of the vehicle while farming vehicles are not even checked or have catalytic converters.
It is time for a change.