Note requirement is to have lights on the bike, not on the person.

Possible scenario:

Cyclist gets taken to hospital after cycling with lights on the straps of his satchel (I’ve seen it). Satchel mysteriously disappears somewhere along the line or otherwise does not come to attention of police. Bike remains at accident spot with no lights on it – assumption is he was cycling unlit so errant motorist not to blame.

This gives a very good summary http://www.dft.gov.uk/pgr/roads/vehicles/vssafety/guidanceaboutlightsonpedalbi4556

re “highway code”.. most of teh code has no legal standing anyway..
lights / bells on bikes you need road traffic act & construction and use legislation, and theres no chance plod will know any of it..