This is one of my pet irritations, and regularly comes up on numerous forums, where a load of urban myths and other b/s is repeated. This usually results from asking a mate in thepub, a MOT tester or Copper who gueses rather than admitting they don't know the answer.
This is compounded as if you half read the lighting regs without checking the exemptions you will wrongly believe that you need a brake light, just as an ignorant traffic cop dis with me!
The bottom line is if you have no front and back lights fitted YOU DO NOT NEED ANY LIGHTS OR REFLECTORS AT ALL. If the law doesn't require it for the test then you don't need it for the road.
You could fit a brake light if you wanted, but would have to make sure that it didn't count as a rear position lamp, perhaps use a single filament bulb?
I have ridden many trials bikes with no brake lights, and do not feel too vulnerable on minor roads.
http://www.flickr.com/photos/24439520@N03/4337899339/The exemptions are below.
The Road Vehicles Lighting Regulations 1989Exemptions—General4.—(1) N/A
(2) N/a
(3)
Nothing in these Regulations shall require any lamp or reflector to be fitted between sunrise and sunset to–(a
)a vehicle not fitted with any front or rear position lamp,.(b)an incomplete vehicle proceeding to a works for completion,.
(c)a pedal cycle,.
(d)a pedestrian-controlled vehicle,.
(e)a horse-drawn vehicle,.
(f)a vehicle drawn or propelled by hand, or.
(g)a combat vehicle..
(4) Without prejudice to regulation 16, for the purposes of these Regulations
a lamp shall not be treated as being a lamp if it is–(a)
so painted over or masked that it is not capable of being immediately used or readily put to use; or.(b)
an electric lamp which is not provided with any system of wiring by means of which that lamp is, or can readily be, connected with a source of electricity.