HI M8teys,,, Well after much perusal the law is clear on this matter.
1. Obvious... if the motorcycle is not intended for road use no number plate so no lights ... but
2. If motor cycle is intended for use on public roads the vehicles lighting regulations are clearly defined:
1989 Road vehicle lighting regulations which came into force on 1st Nov 1989 state
Requirements about the use of front and rear position lamps, rear registration plate lamps, side marker lamps and end-outline marker lamps
24.—(1) Save as provided in paragraphs (5) and (9), no person shall–
(a)use, or cause or permit to be used, on a road any vehicle which is in motion–
(i)between sunset and sunrise, or
(ii)in seriously reduced visibility between sunrise and sunset; or
(b)allow to remain at rest, or cause or permit to be allowed to remain at rest, on a road any vehicle between sunset and sunrise
unless every front position lamp, rear position lamp, rear registration plate lamp, side marker lamp and end-outline marker lamp with which the vehicle is required by these Regulations to be fitted is kept lit and unobscured.
and further reading of the legislation and law is referred to forthwith ..under the RVL Act
..Regulation 18 ...Schedule 1 ...Table 2 refers ...so the bottoms line is
Yes.... the little number plate illumination is required legally for the vehicles use on roads to which the public
use and have access....( in the hours of darkess .... half an hour after sunset and half an hour before dawn )
Please note as far as I have researched the lighting laws have not been appealed or ammended since Nov 1989..
