Apparently it is a legal requirement in the UK for bicycles to be fitted with lights for night riding. I'd have thought it was also more about common sense.
Of course, most of the people in Britain who ride bikes at night are generally thieving little toerags who like to nick stuff from cars, commit rape, muggings and other offences (this excludes working people obviously).
Found this:
LEGAL REQUIREMENTS FOR BIKES
The main law for bikes is currently BS6102, probably soon to be superseded by new CEN standards, but this is for retail use only ie bikes must meet those minimum standards at the point of sale.
Bikes ridden at night need front and rear lights, flashing or steady.
At night a bicycle must also be fitted with a red rear reflector (and amber pedal reflectors, if manufactured after 1/10/85).
At the point of sale (ie shops) bikes now have to come fitted with bells but there's no legal requirement for them to be fitted to bicycles no longer on shop display.
The Highway Code does not stipulate that bells must be used. It states: "Be considerate of other road users, particularly blind and partially sighted pedestrians. Let them know you are there when necessary, for example by ringing your bell."