Here you go, it's some requirement
PBSR requirements
One might suppose that the remaining provisions of this regulation must be comparatively trivial, and so they are. Every new bicycle has to come with:
Any hand-operated brakes arranged left-hand rear, right-hand front
A bell
White or yellow reflectors on both sides of each wheel or tyre
A white wide-angle front reflector, or a front lamp
A red wide-angle rear reflector
Yellow reflectors front and rear on each pedal
The reflectors (or front lamp) required above must be of a specification that is approved by UK Lighting Regulations.
A bike that is sold fully assembled must come exactly so, with all these things fitted as described. But a bike that is sold as a kit, or with some parts un-assembled (perhaps just these parts), merely has to be capable of being assembled like so. In that case it must come with assembly instructions plus any special tools.
http://www.ctc.org.uk/DesktopDefault.aspx'tabID=4072I think this it just for new bikes sold with the intention of using on the roads