It's quite legal - at least for older bikes - I'm not sure about moderns. Our vintage Ariel has no lights and neither does our HT. Even with lights riding older bikes after dark is risky nowadays round here. We seem to have a special brand of 4-wheel idiot who doesn't know what a dipswitch is for and who can't get their headlights set up or working properly either.
I have an XSR700 for after dark and a Jawa Velorex sidecar outfit for when there's too many/too much to fit in/on a solo. Electric start, electronic ignition, pumped oil, sidecar wheel brake - great fun.
HI you can ride a modern motorcycle with no lights all you need is a brake light you you get daylight M O T and if you have a bike after 1954 you need a brake light before that yon can have no light i have 3 bikes running on daylight mot just got a brake light
Actually the year from which brake lights are compulsory is 1936. I believe they were only compulsory on new bikes from 1953 - a rare example of retrospective legislation. Quote from MOT rules:
Exemptions If a stop lamp is fitted, it must meet the requirements of this inspection, but need not be fitted to a machine which: a. cannot exceed 25mph, or b. was first used before 1 January 1936, or c. was first used before 1 April 1986 and which has an engine capacity of less than 50cc.
I'm considering fitting a battery powered LED bicycle brake light on my flat tank Sunbeam just for safety as they are easily removable. All my 1930s bikes including my Red Hunter have been retrofitted quite easily.