18. For the purposes of these Regulations a vehicle which was first registered on or after 1st January 1973 shall be treated as if it was first registered before that date if—
(a)it is an exempt vehicle for the purposes of paragraph 1A(1) of Schedule 2 to the Act(1), or
(b)not being such a vehicle, it was constructed before 1st January 1973.
Paragraph 1A was inserted by the Finance act 1996, s. 19, and amended by the Finance Act 1998, s. 17.