Unimog Club UK

Very grey area, but this is basically the rules as far as I'm aware:

If the vehicle is classed as an agricultural VEHICLE/MACHINE you are aloud to carry a load on the load bed as long as it is your own produce for your own use, and you aren't hauling goods.
However, if the vehicle is registered as a TRACTOR you aren't aloud to carry any produce on the load bed, but you can tow a trailer with your produce on. this is because a TRACTOR is strictly classed as an implement carrier only.