13. Regulation 28 (Seats) shall not apply—
(a)in so far as it consists of paragraph (1)(d) in the case of a vehicle registered before 1st April 1959 if all the passengers' seats in the vehicle are so fitted—
(a)that no part of the back rest of any seat is less than 1.37 metres from the corresponding part of the back rest of the seat facing it; and
(b)there is in relation to every transvere seat in the vehicle a clear space of at least 660 millimitres in front of the whole length of the top of the back rest of that seat measured from the centre of each complete length of the seat allowed for the accommodation of a seated passenger in accordance with condition (b) of the said paragraph (1) but disregarding any handles or grips which do not project more than 105 millimetres from the back rest;
(b)in so far as it consists of paragraph (1)(f) and (g) in the case of a vehicle registered before 1st April 1959 if no seat placed over the arch of a wheel of the vehicle is in such a position as to cause discomfort to passengers;
(c)in so far as it consists of paragraph (1)(h) in the case of a vehicle registered before 1st April 1959 if, as respects any transverse seat in the vehicle which is so placed that a passenger seated upon it is liable to be thrown through any entrance to or exit from the vehicle or down a stairway in the vehicle, an effective screen or guard is placed so as to afford adequate protection against that occurrence to a passenger occupying that seat.