6. At the end of paragraph 4 (agricultural engines) (which becomes sub-paragraph (1)) add—
“(2) In sub-paragraph (1) above “agricultural engine” means a vehicle which—
(a)is designed and constructed primarily for use otherwise than on roads,
(b)is designed, and used, solely for purposes relating to agriculture, horticulture or forestry,
(c)is used on public roads only for proceeding to and from the place where it is to be or has been used for those purposes, and
(d)when so proceeding does not carry any load except such as is necessary for its propulsion or for the operation of any machinery built-in or permanently attached to the vehicle.”.