Hi Lee, hope you’re well. The information you require is documented here, specifically regulation 14A for an import vehicle (I have this document printed off and in my glovebox just in case!).
The Z32 (import) falls into this category:
“Size and spacing of characters: special cases
14A.—(1) This regulation applies in relation to any vehicle imported into the United Kingdom which—
(a)does not have European Community Whole Vehicle Type Approval; and
(b)is so constructed that the area available for the fixing of the registration plate precludes the display on the plate of a registration mark in conformity with the requirements of regulation 14.
(2) In relation to a vehicle to which this regulation applies—
(a)each character in the registration mark must be 64 millimetres high;
(b)the width of each character of the mark, other than the letter “I” and the figure “1”, must be 44 millimetres;
(c)the width of every part of the stroke forming a character in a mark must be 10 millimetres;
(d)the spacing between any two characters within a group must be 10 millimetres;
(e)the vertical spacing between groups of characters must be 5 millimetres;
(f)the width of a margin between the mark and the top and lateral sides of the registration plate must be not less than 5 millimetres;
(g)the space between the bottom of the mark and the bottom of the registration plate must be not less than 13 millimetres; but, within that space, the space between the bottom of the mark and the top of the name and postcode of the person by whom the plate was supplied must be not less than 5 millimetres.”