For information on the current, often confusing, state of UK law
(High Visibility Standards http://www.beseenonabike.com/bsoab/beseenonabike_legal_standards.htm )
The Euro-friendly clause
Thanks to a European Directive of a few years ago, wherever a British Standard (BS) is referred to, equivalent standards from other EC countries must now also be recognised, but only if they provide an equivalent level of safety etc. It’s not exactly clear which do. However Germany has arguably the strictest cycle lighting laws in Europe so we consider it safe to use equipment that is marked accordingly, with a “K~number”.
It should also be noted that wherever a British Standard is referred to, that reference applies to a specific edition. In the case of BS6102/3, that is the 1986 edition, as amended on 15th April 1995 and again on 1st September 2003. These amendments removed the filament bulb design restrictions, so that lamps may now get their light from LEDs – or indeed anything else!